WASHINGTON (AP) _ Two weeks of NATO airstrikes have ``rattled'' Yugoslav President Slobodan Milosevic and hurt morale among his armed forces, which are struggling with fuel and ammunition shortages and bombed-out command centers, Pentagon officials said.

Serb air defenses remain a threat to NATO aircraft, however. Widely scattered tanks and troops accused of leading an ethnic cleansing campaign against ethnic Albanians in Kosovo are still proving difficult to strike despite a stepped-up allied air campaign that was taking advantage of clear skies today to hit more targets, U.S. officials said Tuesday.

``We have evidence of units that had to go into holding operations or holding patterns because of shortages of, specifically, gas and ammo,'' said Rear Adm. Thomas Wilson, director of intelligence for the Joint Chiefs of Staff. He acknowledged few troops or tanks have been struck, mostly because they're hiding in mountainous terrain or are too close to innocent refugees.

Meantime, the acting parliament speaker in Cyprus said he would go to Belgrade today to work for the release of three U.S. soldiers who were captured by Serbs while patrolling the Yugoslav-Macedonian border. Dawn Reliford, sister of one of the three, Staff Sgt. Christopher J. Stone of Smiths Creek, Mich., said the family had been told of the effort by Pentagon officials.

The Cypriot official, Spyros Kyprianou, said he had conducted ``informal consultations'' for several days. In Washington, Sandy Berger, President Clinton's national security adviser, said he was aware of the effort to gain the release of the three ``but I can't confirm that is going to take place.''

Wilson cited ``anecdotal reports that morale is declining'' in the Serb military following this past week's most devastating U.S. cruise missile and bomb strikes on army and police headquarters, command centers and fuel and ammunition depots throughout Yugoslavia and an intelligence training facility outside Belgrade. Wilson didn't offer any estimates of Serb military casualties.

In a sign that Milosevic is feeling the effects of NATO airstrikes that began March 24, he announced a unilateral cease-fire Tuesday and offered to allow ethnic Albanians back into Kosovo.

After pushing about half the 2 million Kosovo population out of the Serbian province since February 1998 _ more than 400,000 ethnic Albanians in the past two weeks _ Milosevic may feel he has changed the situation on the ground to his advantage. Previously, Kosovo was about 10 percent Serbian.

But the Clinton administration and other NATO nations quickly rejected the cease-fire offer, calling it a sham and insisting that Milosevic pull back his forces, allow refugees to return home under NATO protection and accept a peace plan giving ethnic Albanians self-rule.

``This offer may be one sign that he is rattled,'' Pentagon spokesman Kenneth Bacon said. ``But we are going to continue to rattle him until he makes an offer that meets our conditions, and he's far away from that right now.''

Intensified NATO airstrikes have led to increased reports of civilian casualties. In the worst case so far, an allied bomb went astray Monday night and hit apartment buildings in the mining town of Aleksinac, about 100 miles south of Belgrade.

Serb television reported at least 12 civilians killed. The Pentagon said a laser-guided bomb from a U.S. plane fell short of its target, a nearby military post housing a Serb artillery brigade, possibly because cloud cover interfered with the guidance system.

The United States has agreed to house as many as 20,000 ethnic Albanian refugees temporarily at the U.S. naval base at Guantanamo Bay, Cuba, to ease the Balkan refugee crisis. Other Europeans countries are taking in some 100,000 _ but only until they can return to Kosovo.

Defense Secretary William Cohen was visiting NATO headquarters in Brussels, Belgium, today to consult with authorities there on the latest Kosovo developments. He was accompanied by members of Congress, including Sens. John McCain, R-Ariz., and Carl Levin, D-Mich.

Secretary of State Madeleine Albright and NATO foreign ministers will meet in Brussels early next week to assess the offensive against the Serbs and reaffirm their determination to forge a settlement for Kosovo, State Department spokesman James Rubin said.

Trying to mend fences Tuesday, Vice President Al Gore telephoned Russian Prime Minister Yevgeny Primakov, who has vigorously opposed the bombing. It was first time the two had spoken since Primakov turned his plane around last month en route to Washington to protest the start of the air campaign.

Gore told reporters on Air Force Two on a trip to California that he spoke with Primakov for about an hour.

``We are trying to limit damage to the U.S.-Russian relationship,'' Gore said. ``He and I have a very good personal relationship. The call was businesslike.''

Berger acknowledged that Gore and Primakov talked about Kosovo. ``The vice president simply made clear to Prime Minister Primakov what it was that NATO expected Mr. Milosevic to do to end this bombing campaign,'' Berger said. ``To the extent Russia or anyone else can convince Mr. Milosevic to accede to these conditions, so much the better.''

Meanwhile, an NBC-Wall Street Journal poll found that almost two-thirds of the American public supports the airstrikes. Just over half, 53 percent, say they would support ground troops if Serbians continue to drive people out of Kosovo. That slight majority of support for ground troops was reflected in polls earlier this week by both Newsweek and ABC News.

That support grows to almost three-fourths, 73 percent, if ground troops is the only way to stop the fighting in Kosovo, according to the NBC-Journal poll released today. The poll of 503 people taken Monday has an error margin of plus or minus 4.5 percent.