Secretary of State Cyrus R. Vance, seeking to defuse concern over a possible U.S. confrontation with Uganda, said yesterday that he believes Americans there "will be safe" after Monday's meeting with President Idi Amin.

"I do not believe it will be a crisis situation. I certainly hope it will not," Vance told reporters after a lengthy meeting at the state Department on variety of topics with U.N. Secretary General Kurt Waldheim.

The White House, in a brief written statement, said the United States welcomes Uganda assurances - given in a radio broadcast and through diplomatic channels - that there is no intention to harm the 240 Americans who were summoned Friday to see Amin.

The White House statement expressed continued concern about the welfare of Americans in the African country and said the United States "looks to Uganda authorities to insure that Americans and other foreigners within that country are protected as is customary under international law.

A special U.S. working group at the State Department continued its round-the-clock monitoring of the Uganda situation, but officials sought to dispel any sense of crisis. There was a feeling among some analysts that Amin was interested in the international limelight, as in some earlier highly publicized challenges to Britain, but not in a showdown with the United States.

A State Department spokesmen has informed the United States that it is taking "all possible steps to protect the Americans on Nganda and that they are in no immediate danger." Bonn has represented U.S. interests in Uganda since Washington closes its embassy in 1973 due to a patten of violence and violations of human rights.

Waldheim, in an interview, said he had offered his "good offices" as an intermediary between the United States and Amin but that he has not yet been asked to take any such action.Waldheim said he met twice within the past few days with Uganda's ambassador to the United Nations to request that an impartial internation investigation be permitted into the deaths on Feb. 16 of Archbishop Janani Luwum and tow senior Ugandan cabinet members, but received no =substantial answer" from Amin.

Amin's summons to the Americans their exist from the country followed President Carter's press conference remarks Tuesday endorsing a U N investigation of "the horrible murderes that apparently are taking place in that country." Carter also said that Uganda's actions "have digusted the entire civilized world."

Waldheim's conference with Vance, which lasted closed to 2 1/2 hours rather than the scheduled hour, concentrated on the Middle East, Cyprus and other long-standing international problems in which both the United Nations and the United States are deeply involved.

Waldheim praised "a new spirit that he found in his White House and State Department meetings, and said he expects "much closer cooperation between the United States and the United Nations than in the past.

The top U.N. official was openly pleased at the extensive attention paid him here, including VIP transportation to and from New York by an Air Force jet, an overnight stay as a state visitor at Blair House, a working luncheon with Carter at the White House and a State Department dinner in his honor hosted by Vance. Waldheim did not receive such treatment from the Nixon and Ford administrations.

Having recently completed a Middle East mission similar to Vance's Waldheim said he, too, expects the reconvening of a Geneva peace conference in the second half of 1977. He said he doubts that a final settlement will be possible within this year, however.