President Carter's decision not to attend Yugoslav President Tito's funeral has disappointed many State Department and White House officials concerned with foreign policy and Yugoslav affairs.

Administration sources said yesterday that many officials in both agencies had hoped the president would go to Belgrade, had urged that he do so, and feared that his absence could weaken U.S. interests in Europe and the Third World, at least in the short term.

These officials also confirmed that the U.S. ambassador to Belgrade. Lawrence Eagleburger, had urged the president's attendance several times in the months since Tito became seriously ill.

Senior White House officials offered a variety of general reasons why the president decided not to go.

But reports from Belgrade and criticism in the European press made it clear that Carter's absence was conspicuous. It reportedly miffed both the Yugoslavs and U.S. allies as a decision too narrowly formed by domestic political considerations at a time of grave international problems.

The attendance in particular, of an ailing Soviet President Leonid Brezhnev in Belgrade -- a move widely seen as a Soviet start on improving ties with the maverick communist state -- also underscored the president's absence.

Explanations of the president's action varied among administration officials.

Senior White House officials, who asked not to be identified, said Carter believed the United States would be ably represented by Vice President Mondale, who has been to Yugoslavia twice before.

Since the president had severely limited his travel in the United States for many months, the officials said, "He felt a foreign trip under these circumstances would be inappropriate.The president has a number of matters, both foreign and domestic, before him that require his attention."

Most importantly, he said, the president has made very clear the U.S. support for Yugoslavia's independence and integrity in the post-Tito era. "We believe the Yugoslavs know who their friends are, who poses a threat to them and who does not," he added.

On two other key points, however, officials told different stories. The White House denied that prior commitments by Carter were the reason, though others said that was the explanation given them.

Carter spent time yesterday afternoon and evening at functions marking the beginning of the new Department of Education, a politically important goal that won him the all-out support of the National Education Association. g

On Friday, the president goes to Philadelphia for his first full-blown trip outside the White House since the Iranian hostages crisis began and since he dropped his Rose Garden strategy of staying in Washington as long as the hostages were held. This would have been canceled by a trip to Belgrade.

White House officials also deny that Carter decided not to go to Belgrade because he did not wish to meet Brezhnev there. Other officials, however, say this was a key part of the internal White House discussions in the months of Tito's illness.

In one view, Carter faced a "nowin" situation if he went. The White House clearly didn't want to meet with Brezhnev because this would have sent the wrong signal to Moscow and the rest of the world regarding the depths of U.S. concern over the Soviet invasion of Afghanistan.

At the same time, if the president went and didn't meet the Soviet leader, the U.S. allies might have been annoyed that Carter failed to take an opportunity to start a new dialogue with Moscow in an effort to cool superpower tensions.

Other administration officials, however, believe this situation could have been handled, that Carter could have made the trip quickly, that it would have done him good at home to be seen in company of the world's leaders and that it would also have avoided all the private criticism in Yugoslavia and among the allies.

As long as the president was staying in the White House over the hostages, it was assumed Mondale would go to a Tito funeral. However, after the aborted rescue mission on April 24, the president announced on April 30 he was now coming out of the White House. Then Tito died on May 4, which suddenly raised the question of whether the president, rather than Mondale, would go. Carter decided, officials say, late Sunday or early Monday, not to go. On Tuesday, it was announced Brezhnev would go.

In previous weeks, Russians in Washington were hinting that Brezhnev probably would not be up to a trip to Belgrade. But U.S. officials said they were keeping track of the Soviet leader and thought he was being rested to improve his health so that he could make such a trip.

"I don't think we got snookered," one official said, "but undoubtedly the president's decision not to go reinforced the Kremlin's effort to get Brezhnev there."

Officials hinted yesterday that Carter would visit Yugoslavia soon, possibly next month.