The Bush administration, which cut off its share of financing two years ago to the United Nations agency handling population control, is seeking to isolate the agency from groups that work with it in China and elsewhere, United Nations officials and diplomats say.

Pressed by opponents of abortion, the administration withdrew its support from a major international conference on health issues this month and has privately warned other groups, like Unicef, that address health issues that their financing could be jeopardized if they insist on working with the agency, the United Nations Population Fund.

The administration also has indicated that it hopes to persuade the United Nations' Latin American caucus to back away from a common position on population and development that was adopted in Santiago, Chile, in March on the grounds that the document's discussion of reproductive rights could be interpreted as promoting abortion.

The actions are part of an administration effort to ensure that international agencies and private groups do not promote abortions overseas. In its first days in office, the Bush administration reintroduced the Reagan-era that critics call the "global gag rule," which denies money to groups that even discuss abortion as an option, except in cases that threaten life or involve rape or incest. 

The Population Fund, known as Unfpa, has long been a favorite target of abortion opponents in Congress and in religious-based organizations, who contend that it assists in coercive abortions in China. The critics prevented American financing of the fund for most of the last two decades, and they have now set their sights on curbing its operations with other United Nations agencies.

The administration's position has frustrated some United Nations officials and family planning advocates, who have complained that advances in education and awareness on reproductive issues are being undermined by the United States, where abortion is legal. 

Those critics, most of whom spoke anonymously because the United States government is the leading contributor to their agencies, charged that the administration was pandering to conservative supporters, and said that doing so placed the United States in alliance with tradition-bound Islamic countries and the Holy See.

Last year, the State Department cut financing to Marie Stopes International, a British charity involved in AIDS programs, because it worked with the Population Fund in China.

In a letter to Secretary of State Colin L. Powell on Friday, four Democratic members of Congress demanded a legal explanation for withholding money from the fund and for the "threatened defunding of the World Health Organization and the United Nations Children's Fund."

Representative Carolyn B. Maloney, a New York Democrat at the fore of efforts to restore support to the fund, said the administration was jeopardizing programs in women's and family health that should not be considered contentious. 

"When will the president's right wing be satisfied - when they close down the U.N.?" she asked, adding that the tough White House stance contrasts with its appeals to the United Nations for help in the Iraq war.

Supporters of the fund deny that it facilitates coerced abortions in China. They say it has made considerable progress in reducing the number of abortions through family planning programs in conjunction with the Beijing government.

Two years ago, the administration appeared to agree. A fact-finding trip for the State Department in May 2002, led by William A. Brown, the former ambassador to Israel, recommended the release of $34 million in American payments. "We find no evidence that'' the Population Fund "has knowingly supported or participated in the management of a program of coercive abortion or involuntary sterilization" in China, it said.

But Mr. Powell, who had praised the agency's activities, abruptly reversed course, contending in a July 21, 2002, letter to Congress that the fund had provided computers and vehicles to Chinese government groups that enforced the country's coercive reproductive policy, which taxes parents who have more than one child. He charged that the fund was in violation of the 1985 law known as the Kemp-Kasten amendment, which prohibits the United States from giving money to agencies involved in coerced abortion or sterilization. 

President Bush withheld the $34 million in 2002 and another payment last year. He has until July 15 to decide for this year's budget.

Conservative religious groups are keeping the pressure on the administration. A group leading the fight against the fund is the Population Research Institute in Front Royal, Va., which calls itself a research and education group that exposes human rights abuses in population control programs. The institute says China's population control policy bullies women through the mandatory use of contraception, forced abortions for those younger than 20 and prison for those who do not appear for examinations. By working with the government, the Population Fund is complicit, critics say. 

The Population Fund's "support consists of public praise for, and misinformation about, China's coercive family planning policy," the institute says on its Web site.

Fund supporters counter that they have nothing to do with abortion policy. Through their programs, they give maternity kits and prenatal care to pregnant women. The administration's cuts, they say, have hurt poor women in China and elsewhere. 

Sterling Scruggs, a former official in charge of external relations for the Population Fund, said his agency was being singled out to make an "ideological" point against abortion. "It reminds me of the McCarthy era," he said. "We're blackballed. They've defunded us, and even that isn't enough. It's unbelievable."

Recent signs suggest that the administration is increasing pressure on the fund in the heat of an election season.

At an informal meeting of the Unicef executive board and donors this month, the administration announced that it could no longer support joint programming with the fund because of concerns that the money could not be kept separate. United Nations officials say that joint programs allow agencies to pool resources, providing advantages in costs and efficiency.

Three federal offices pulled their support in April from the 31st annual conference sponsored by the Global Health Council. The conference, which was the first week of June, included speakers from the fund and the International Planned Parenthood Federation, its organizers said. Unlike the Population Fund, Planned Parenthood openly supports abortion services where they are legal.

Dr. Nils Daulaire, the president of the Global Health Council, an alliance of health professionals, said he was notified by the United States Agency for International Development, the Department of Health and Human Services and the Centers for Disease Control and Prevention that no federal money would be made available for the conference, citing "statutory duties."

Dr. Daulaire said the withdrawal resulted in the loss of more than a third of the conference's $1 million budget weeks before the event. Arthur E. Dewey, the assistant secretary of state in the Bureau of Population, Refugees and Migration, was not available for comment. 

At a meeting in March of family planning lobbyists and others, he said the department's goal was to reach a legal interpretation that would allow financing of the fund, two participants in the meeting said.

But Mr. Dewey warned that advocates of the fund should not try to hitch their fortunes to other agencies in China, including Unicef and the World Health Organization, to pull those larger agencies into the abortion dispute and "tar and feather" them, the participants said.