U.N. Secretary General Javier Perez de Cuellar said today that his two days of talks with Vietnamese leaders had "made progress" toward eventual negotiations on settling the six-year-old conflict in Cambodia and on resolving problems between Vietnam and the United States.

In a joint news conference with Vietnamese Foreign Minister Nguyen Co Thach, Perez de Cuellar said he had received "very important clarifications" of Vietnamese proposals for settling the Cambodian conflict. He declined to give details of the clarifications, however, and cautioned against being "over optimistic" and raising false hopes on the issue.

"If clarifying positions brings negotiations closer, then we have made progress," Perez de Cuellar said.

He also said he had raised several questions with Vietnamese leaders at the request of the U.S. government and that "I can assure you I have made significant progress" on four points.

According to a U.N. source, these points include U.S. efforts to account for about 2,500 American servicemen missing in action during the Vietnam war, to bring out Amerasian children living in Vietnam, to negotiate a deal to take in reeducation camp inmates detained for past associations with the United States or the former South Vietnamese government and to resolve the case of an American yachtsman captured off southern Vietnam last year.

"I think you will see progress on the MIA missing in action issue in the near future," the source said. An American team is to visit Vietnam shortly for talks with Vietnamese specialists on the matter.

During the news conference Foreign Minister Thach reiterated his recent remarks that the United States has a role to play in bringing about a settlement in Cambodia. He said U.S. involvement in efforts to "solve any question in Southeast Asia are welcome."

He added, "If the United States can make war here, they can easily make peace here." Vietnam is preparing to celebrate the 10th anniversary of its capture of Saigon and defeat of the U.S.-backed South Vietnamese government in April 1975.

Western diplomats interpreted Thach's remarks as part of a Vietnamese bid to get Washington to use its influence with Thailand toward achieving Hanoi's main aim of eliminating the Khmer Rouge, the widely reviled communist guerrilla group that poses the main threat to Vietnam's military occupation of Cambodia.

Vietnam and its allies in Laos and Cambodia issued a communique this month calling for the elimination of the Khmer Rouge in conjunction with a Vietnamese withdrawal from Cambodia followed by "free elections" supervised by foreign observers. Noncommunist Southeast Asian countries opposed to the Vietnamese occupation, notably neighboring Thailand, have been seeking clarifications of the proposals through Perez de Cuellar.

The U.N. chief left today for Bangkok to brief Thai leaders on his talks here and convey the Vietnamese clarifications. On Friday he is scheduled to meet Prince Norodom Sihanouk, who heads a U.N.-recognized coalition composed of three Cambodian resistance groups including the Khmer Rouge.

Perez de Cuellar then is scheduled to visit Indonesia, Malaysia, Singapore, Australia and New Zealand.

Thach disassociated the Cambodian question from the MIA issue, stressing that the latter was a "humanitarian issue" between Vietnam and the United States and that Hanoi was pursuing efforts to resolve it "free of charge."

On the question of reeducation camp inmates, a U.N. source said, the Vietnamese told Perez de Cuellar that they were prepared to negotiate with the United States but that they considered the matter a political rather than humanitarian issue.

In recent weeks Vietnam has appeared to scotch U.S. efforts to reach a deal on taking in the prisoners by demanding that guarantees be given to prevent their engaging in opposition activities once they reach the United States. U.S. officials have said the United States is constitutionally unable to give such guarantees.