The Clinton administration has defused an effort by European allies to restore commercial air service to Yugoslavia, a senior official said yesterday. But European foreign ministers approved $5 million in fuel oil assistance for Serbia, despite U.S. concerns that the aid could benefit Yugoslav President Slobodan Milosevic.

U.S. officials are eager to preserve the flight ban as part of their strategy to isolate Milosevic and eventually force him from power. But several key allies are pressing to restore air service between Belgrade and European capitals, which was suspended last year during the buildup to the Kosovo crisis, the official said.

Last week, U.S. Secretary of State Madeleine K. Albright spoke with some of her European counterparts--including British Foreign Secretary Robin Cook, French Foreign Minister Hubert Vedrine and German Foreign Minister Joschka Fischer--to warn against any weakening of economic sanctions against Yugoslavia.

She was partly successful. Meeting in Luxembourg yesterday, foreign ministers from the 15-member European Union agreed to leave the commercial flight ban in place, at least for now.

Meanwhile, the ministers approved $5 million in fuel oil assistance destined for two Serbian cities controlled by political opponents of Milosevic. Although Albright did not specifically object to the plan, she expressed concern that such assistance, if not carefully monitored, could help shore up Milosevic's regime, according to State Department spokesman James P. Rubin.

"We support the principle of giving aid to the opposition, and we support this latest development as far as it goes," Rubin said. "However, our ultimate judgment about the wisdom of this kind of a project will depend on its implementation. We remain concerned about doing anything that would weaken the overall sanctions regime."

At their meeting yesterday, the EU foreign ministers agreed to ship fuel oil to Nis and Pirot, two cities whose petroleum refineries were destroyed during the 78-day NATO bombing campaign last spring.

"People are going to freeze otherwise," an EU diplomat told Reuters. EU diplomats also contend that the assistance would boost political opposition parties that could emerge as a democratic alternative to the Yugoslav president.

U.S. officials say they have no objection to the distribution of humanitarian aid, such as food and medicine, inside Serbia. The United States has provided $35 million to the United Nations and various relief agencies for use throughout Yugoslavia. In addition, the Clinton administration has earmarked $12 million to strengthen pro-democracy forces in Serbia, such as labor unions and an independent press.

A senior U.S. official expressed skepticism, however, about whether the fuel oil will be needed this winter. The official also noted that providing oil could free up resources within the Yugoslav government for other purposes. "Will it be properly used? How will you monitor it? Are you sending the right signal?" the official quoted Albright as asking the EU ministers.

"We don't want to see a situation developing where what began as a humanitarian gesture gradually creates a cascade to ending pressure on the regime," the official added. "She's tried to put an outer limit on what they want to do."

Besides the fuel oil plan, several key European allies--the official declined to specify which ones--argued during the buildup to the Luxembourg meeting for an end to the commercial flight ban. But, after Albright's intervention, "they did not put it forward for now," the official said.

If the European foreign ministers wanted to demonstrate solidarity with the opposition to Milosevic, they were disappointed. At the last minute, 10 key opposition politicians, including such familiar figures from recent street demonstrations as Vuk Draskovic and Zoran Djindjic, canceled plans to attend the Luxembourg meeting.

Declining to board the aircraft that carried 20 other opposition figures from Belgrade, the top leaders said they would not participate in the meeting because the EU wanted them to pledge that if they come to power they will extradite Milosevic to face war crimes charges at an international tribunal in The Hague.

The opposition leaders said agreeing to this demand would play into Milosevic's strategy of portraying his adversaries as Western puppets--or "bootlickers," as the Serbian leader called them yesterday.

Trueheart reported from Paris.