Foreign Aid for Family Planning
An overwhelming majority believes that population growth is a serious contributor to the economic problems of the developing world. A very strong majority supports the US providing aid to assist people in poor countries with family planning. Support is more mixed, however, when the goal is framed in terms of the goal of getting developing countries to reduce their birthrates.
An overwhelming majority believes that population growth is a serious contributor to the economic problems of the Third World. Seventy-one percent (43% strongly) agreed that "Too much population growth in developing countries is holding back their economic development" (Belden & Russonello, September 1998). Only 25% disagreed. This is higher than in February 1994, when the same question was asked about "the world" rather than "developing countries," and 55% agreed, 24% strongly (41% disagreed). 
A more modest majority sees population growth as contributing to political instability. In 1994, 57% thought "rapid population growth in developing countries is frequently an underlying cause of civil wars and regional conflicts"; by 1998, this was down to 51%, perhaps due to the diminishing number of media reports on such wars compared to 1994 (both polls, Belden & Russonello). 
Support for Aid for Family Planning
When asked directly about providing aid for family planning, support tends to be very high. Most recently (June 2004), the Chicago Council on Foreign Relations found 76% in favor of "aid for women's education in poor countries to help reduce population growth."  With regards to Africa, a July 2002 question by Kaiser Foundation and Harvard School of Public Health found that 75% thought "providing family and population control" should be a high priority (44%) or moderate priority (31%) for U.S. spending on health care in Africa. (For more on this and related topics, see Africa: Aid for HIV/AIDS Crisis in Africa.)
There is broad consensus among Americans that family planning, as such, is a service that should be universally available. A near-unanimous 92% agreed (69% strongly) that "All couples and individuals should have the right to decide freely and responsibly the number, spacing and timing of their children and to have the information and the means to do so" (Belden & Russonello, September 1998). In the same poll, 68% knew that family planning was not "already available to most people in all parts of the world today." 
When asked to rate how high a priority family planning should be in US aid programs on a scale of 1 to 10, with 1 meaning the lowest priority and 10 being a top priority, family planning scores quite high. In a February 2000 poll, for "Making birth control available to people in other countries so they can choose the number of children they have" the mean rating was 6.9, with 39% rating it at 10 (Belden, Russonello and Stewart). In September 1998, asked about "possible goals for US government assistance to other countries," the mean response was also 6.9 to the goal of "Helping women in poor countries avoid unintended pregnancies" with 30% giving it a rating of 10 (Belden & Russonello). In the same poll an overwhelming 88% favored "programs to encourage men to take an active role in practicing family planning." When respondents were asked in March 1993 to rate a variety of types of foreign aid on a 1-to-10 scale, "education on family planning and providing birth control" got a 7.1 median score (Intercultural Communication, Inc.). Related questions that do not focus directly on family planning get slightly lower scores.  (For the relationship to other women's issues, see also Women's International Issues: Approaches to Family Planning.)
When told explicitly that family planning does not include abortion, support is also very high. In the 1998 Belden and Russonello poll, respondents were first given a definition of family planning, as follows:
I am going to use the term "family planning" and define it to mean: having the information and services, including birth control and contraception, to determine if and when to get pregnant, and getting help with infertility problems. In this definition, family planning does not include abortion.
Hearing this definition, 80% (45% strongly) said they favored "the US sponsoring voluntary family planning programs in developing countries" (18% opposed). In February 1994, the same question was asked but the definition above was not given: a much lower 59% favored such programs then, with 37% opposed. 
When Americans are asked about the idea of withholding foreign aid funds where family planning is involved, a modest majority rejects this idea even if the term "family planning" is not defined in the question. In December 2001 53% opposed the "proposal ...[of] withholding foreign aid from any foreign government or organization that spends part of its money on family planning programs"; 41% supported this (Greenberg/Public Opinion Strategies). [6a]
When aid for family planning is placed in the context of spending on foreign aid, cuts in such spending may elicit plurality support. The 1998 Belden and Russonello poll told respondents that "Since 1995 the US Congress has voted to reduce the US contribution to family planning in developing countries by 30%"; asked whether they approved or disapproved this action, 49% approved and 45% disapproved.  However, this response seems to be driven largely by the fact that Americans grossly overestimate the amount of US foreign aid and are thus responsive to the idea that Congress would cut some aspect of it.
More importantly, when given information about the cost of US foreign aid for family planning, three-quarters of respondents wanted to maintain or increase it. In January 1995 PIPA asked, in the context of a battery of questions on different parts of the US foreign aid program:
For family planning, to help poor countries limit the growth of their population, the US spends 450 million dollars, about 86 cents for the average taxpayer. For family planning, would you favor increasing spending, cutting spending or keeping it the same?
Seventy-four percent wanted to increase (36%) or maintain (38%) family planning aid; only a quarter wanted to cut it. 
Ambivalence About the Goal of Reducing Birthrates
While support for assistance for family planning is high, the support for using aid for the goal of reducing birthrates is more mixed. The reason for this ambivalence may well be found in the response to a 1998 Belden and Russonello question that asked: "Do you agree more with those who say the United States should encourage developing countries to lower their birthrates, or more with those who say it is inappropriate for us to do this because it may offend other people's cultures?" A slight majority of 52% said they thought this was inappropriate, while 42% said it was not. Interestingly, the percentage concerned about this issue has risen. In 1994 only 41% said they thought it was inappropriate, while 55% were not so concerned. 
There is also a strong and growing consensus that there should not be any encroachment on the right to have children. In February 1994 68% agreed (37% strongly) with the statement: "People should feel free to have as many children as they can properly raise" (30% disagreed). When this was asked again in September 1998, agreement had gone up to 76% (50% strongly) and only 23% disagreed (Belden & Russonello).  Presumably the response to this question is colored by a rejection of coercive birth control practices associated with China, but it is also an indication that Americans feel that the US should not take the position of pressuring individuals to refrain from having children.
These feelings may well explain lower levels of support for aid programs that are framed in terms of the goal of lowering birthrates as compared to those that are framed in terms of helping people in poor countries with family planning. In the September 1998 Belden and Russonello study, when respondents were asked to rate goals for US assistance abroad on a scale of 1 to 10, "Education on family planning and providing birth control" was rated at 7.1 and "Helping women in poor countries avoid unintended pregnancies" was rated at 6.9. However, "Helping countries slow their rate of population growth" scored a lower score of 6.3, while in 1994 it was rated 5.9. 
This pattern also explains the Chicago Council on Foreign Relations' July 2004 finding: 70% favored "aid for birth control in poor countries to help reduce population growth," while only 25% were opposed. The specific mention of "birth control" probably clarified the voluntary nature of the efforts to respondents. [11a]
While the support for aid for family planning can be overwhelming, receiving more than 80% support, questions that speak of aid for limiting population growth find a more modest majority. Thus 54% favored "an increase in US economic aid and technical assistance to help developing countries slow their population growth" (39% opposed) and 55% favored "the US sponsoring programs overseas to help other countries slow their population growth" (42% opposed; Belden & Russonello, February 1994). 
Questions About Effectiveness
A few older findings suggest that many Americans have been unsure whether aid targeted to population problems tends to be effective. In 1993 Intercultural Communications, Inc. asked how much of an effect respondents thought "US assistance to Third World countries" had had on "reducing population growth in those countries." Sixty-five percent at that time thought its effect had been "not much" or "none," while only 29% thought it had had a "great" or "some" effect.  This question was one of a series of ten questions about the effect of US assistance on various problems. Since US assistance was seen as more effective in all nine other areas, we cannot attribute the sense of aid's ineffectiveness on population growth to Americans' general doubts about foreign aid. It seems more likely that Americans then felt population growth was a very serious problem on which virtually no headway was being made. This would be consistent with the later finding (Belden & Russonello, September 1998) that the public considerably overestimates the rate of world population growth (see "Attitudes About World Population Growth").
Another question suggests that a majority may put more stock in aid for education, and the possibility that it may indirectly affect birth rates. Gallup asked in April 1992 which of a list of measures "would be the most effective long-term approach to solving overpopulation in developing countries" and listed four approaches. A 55% majority chose "increasing education, including literacy around the world." "Increasing family planning for couples" was a distant runner-up at 20%, while "improving health care for the poor" and "improving women's status in underdeveloped countries" trailed at 10% and 4% respectively. 
Support Appears to Be Altruistic
Apparently support for aid for family planning is derived from altruistic concerns rather than interest-based concerns. As discussed above, very strong majorities said that population growth is limiting the economic development of developing countries and support for aid for family planning is high.
However, arguments in favor of action to reduce population growth based on national self-interest do not elicit strong support. When Gallup asked simply "Do you think it's the United States' interest to help slow the rate of population growth overseas, or not?" just 50% said it was in the US's interest and 44% said it was not (April 1992). The argument that "slowing population growth in other countries will reduce immigration into the US" elicited agreement from just 45%, while 50% disagreed (Belden and Russonello, February 1994).