Vietnamese Foreign Minister Nguyen Co Thach predicted today that the communist and noncommunist nations of Southeast Asia will begin talks within the next several months about a settlement of the war in Cambodia.

Thach said in an interview that he began preliminary discussions in New York within the past week with noncommunist foreign ministers of the Association of Southeast Asian Nations (ASEAN) on the date, place and agenda for a first round of talks on the Cambodian dispute.

The Vietnamese minister also proposed negotiations with the United States at a political level about the resettlement here of some 8,000 to 9,000 inmates of Vietnamese "reeducation camps."

The inmates were associated with the U.S. war efforts or those of the former Saigon government. The Reagan administration agreed last month to accept up to 10,000 prisoners and family members, taking up an offer made by Vietnam more than two years ago.

U.S. representatives presented a plan for resettlement of the camp inmates to Thach's deputy, Le Mai, in Geneva last week, but Thach expressed a clear preference for negotiating the issue himself during his current visit to the United Nations General Assembly.

He said he also wishes to discuss speeding the search for Americans missing in action from the Vietnam War, expediting the departure of Amerasian children from Vietnam and "other issues which concern both parties" with U.S. authorities before he leaves New York Oct. 21.

In advance of any additional discussion, Thach said, Vietnam has agreed to another visit by a U.S. technical team on the MIA issue within the next six weeks. He suggested that this U.S. visit to Hanoi could provide the occasion for further technical exploration of the question of resettlement from the Vietnamese reeducation camps.

State Department officials said that there were no plans at present to meet with Thach during his stay but that his comments would be studied closely.

In his discussion of both regional and bilateral issues, Thach seemed more positive and conciliatory than in previous public statements.

A Southeast Asian diplomat expressed doubt about the sincerity of Thach's proposals, saying he believes they are intended to "create the impression that some progress is going on" in order to affect the annual General Assembly vote on the Cambodian question this month.

Thach said that the next step in diplomatic discussions about Cambodia will be to arrange a further meeting between himself and Indonesian Foreign Minister Mochtar Kusumaatmadja, who has been designated by ASEAN to take the lead in dialogue with Vietnam. Thach and Mochtar met last Saturday in New York, before the Indonesian left for Canada and home.

"It is possible now" that talks will begin, Thach said. "Not it could be, but it will be. It is not a question of days or weeks, but not a question of years." He predicted that the process will begin within "some months."

Thach said both sides understand that Vietnam's proposals as well as ASEAN's must be considered in any serious discussion of the Cambodian issue.

The Vietnamese foreign minister added that, despite skepticism in the West, Vietnam had begun a process of withdrawing its forces from Cambodia in mid-1982. "In five to 10 years we will withdraw most of our forces" and leave the Vietnamese-backed Cambodian government of Heng Samrin in place, Thach said.

He claimed that one-sixth to one-fifth of the Vietnamese troops have been withdrawn already, although he would give no precise numbers. A State Department official said the United States estimates that the Vietnamese occupation force of about 180,000 in mid-1982 has been reduced by 10,000 to 20,000 now, but that "their combat capabilities have been increased."

Turning to the U.S. role nearly 10 years after the fall of Saigon, Thach said, "We have watched the policy of the United States. We think it has an interest to have peace and stability in Southeast Asia, but up to now the United States has been a little lazy" in pursuing this.

"We welcome any efforts by the United States to bring about peace in Southeast Asia. We hope the United States could contribute . . . and play a more active role. We will cooperate with the United States in this course."

Regarding the release of Vietnamese still in reeducation camps, whom he referred to as "criminals," Thach said Vietnam will insist on guarantees that these people "will not come back or do harm to my country."

Secretary of State George P. Shultz appealed to Vietnam on Sept. 11 to show "good will and cooperation" in resettling "political prisoners" from the reeducation camps during the next two years and permitting Asian-American children and qualifying family members to leave in the next three years.

Thach said the remaining Amerasian children could leave as quickly as three months, if the United States would expand its immigration quotas to receive them.