ROME -- The United States has intensified efforts to force major institutional reforms in the United Nations' Food and Agriculture Organization (FAO) at the same time that the agency's director has said it is facing a "perilous" economic crisis.

The Reagan administration informed the Rome-based agency last week that it will withhold funding until the FAO agrees to reforms favored by the United States, which the organization voted down last November.

The United States, which traditionally had contributed 25 percent of the organization's annual budget -- most recently $437 million -- owes FAO a total of $67 million on its 1986 and 1987 assessments, plus $60 million it was asked to pay toward this year's budget.

The latest U.S. refusal to help bail out the U.N. agency -- which is involved in helping agricultural development in the Third World, including famine-ridden Ethiopia -- was delivered by U.S. Ambassador to the FAO Fred Eckert last week during a meeting of permanent representatives to the organization from its 158 member countries, U.S. and European sources said.

The sources said Eckert delivered his message after the FAO's controversial director general, Edouard Saouma, described the approximately $127 million owed by the United States as "equivalent to more than half the budget of the organization for 1988."

Saouma won reelection to an unprecedented third six-year term last November despite the opposition of the United States, Canada and other western donor nations. He said that when Washington first withheld payments in 1987, the organization had enough financial reserves to cushion the blow.

"Now, we have no reserves left -- indeed, we have carried forward a deficit of $35 million," Saouma, a 60-year-old Lebanese Christian, told the permanent representatives.

"Last time, we managed to avoid making program cuts corresponding to the full amount of the U.S. shortfall -- but in doing so we used up all our reserves," he said. "This time, we shall have to make cuts equal to the U.S. nonpayment, or we will have to borrow."

According to western diplomats here, Britain, Australia and Canada also have suspended payments to the agency. All three are part of the Camberly Group of western donors, named for their original meeting place in Britain, that have joined Washington in pushing for a greater voice in how their money is spent by the organization.

The 11-nation Camberly Group, also includes the Scandinavian countries, West Germany, Japan, the Netherlands and Switzerland. They met in Oslo this week to try to decide on a common position on proposed reforms.

Although the United States is not a member of the Camberly Group, it coordinates its position with the group's members, and Eckert attended the Oslo meeting.

Washington and the Camberly Group sought to block Saouma's reelection last November, much as they successfully opposed the reelection last year of Senegal's Amadou Mbow, the director general of the U.N. Educational, Scientific and Cultural Organization.

The West's opposition to Saouma is based less on ideology than on his management style, including his use of a $63 million emergency fund without seeking the approval of the FAO governing body.

The effort to unseat Saouma failed in part because France and the Organization of African Unity stuck by him, even though Saouma's challenger was a respected African agronomist from French-speaking West Africa, Benin's Moise Mensah.

Unable to oust Saouma, the western donors have focused on implementing reforms that would curb his power and give more influence to the developed countries that pay 70 percent of the FAO budget.