Nearly two-thirds of Americans support an agreement to ease economic sanctions on Iran in exchange for restrictions on its nuclear program. But many fewer - barely more than a third - are confident that such a deal would prevent Iran from developing nuclear weapons.

Sixty-four percent in the latest ABC News/Washington Post poll support a diplomatic agreement to limit Iran's nuclear program, with three in 10 opposed - a result that marks a longstanding preference, all else equal, for diplomatic rather than military responses to international disputes.

See PDF with full results and charts here.

Still, as the U.S. and other world powers prepare to resume talks with Iran this week, there's also broad skepticism about a deal: Six in 10 Americans are not confident that it would prevent Iran from developing nuclear weapons, including a third who are not confident "at all."

Lack of confidence influences support for an agreement: Among those who have no confidence it would produce the desired result, just 38 percent support a pact. Among all others, support jumps to 80 percent in this poll, produced for ABC by Langer Research Associates.

GROUPS - Political views also inform positions on Iran. Seventy-two percent of Democrats support a diplomatic pact vs. 63 and 57 percent of independents or Republicans, respectively - though it's still a majority in each group. Seven in 10 liberals and moderates alike are in support, declining to 55 percent of conservatives, including 45 percent of "very" conservatives.

Additionally, while half of Democrats say they're not confident an agreement would prevent Iran from developing nuclear weapons, that rises to 62 and 70 percent of independents and Republicans, respectively. Conservatives also are much more apt than liberals or moderates to lack confidence in a deal; indeed 78 percent of strong conservatives don't think it'd work, with 57 percent of them not confident at all. Similar results hold for strong supporters of the Tea Party political movement.

Although views don't significantly differ by gender, single women are 11 percentage points more likely than married women to support a deal with Iran, and 19 points more likely to be confident that it might work. And confidence peaks at 52 percent among young adults, compared with just 32 percent among those 30 and older.

METHODOLOGY - This ABC News/Washington Post poll was conducted by telephone Nov. 14-17, 2013, in English and Spanish, among a random national sample of 1,006 adults, including landline and cell-phone-only respondents. Results have a margin of sampling error of 3.5 points, including design effect.

The survey was produced for ABC News by Langer Research Associates of New York, N.Y., with sampling, data collection and tabulation by Abt-SRBI of New York, N.Y.