An Army lieutenant colonel, who won the Medal of Honor, and a Special Forces sergeant are among those who have filed statements in an unusual lawsuit demanding that President Reagan use "proper" means to free U.S. servicemen they believe are still imprisoned in Southeast Asia.

"I am personally convinced that there are in fact live Americans in captivity and that there is an ongoing effort by the Defense Intelligence Agency to ignore such reports," said Lt. Col. Robert L. Howard in his affidavit added to the suit filed in federal court in Fayetteville, N.C., on Sept. 4.

The suit also asks that the 2,464 U.S. servicemen listed by the Pentagon as missing be treated as a single class of plaintiffs.

Howard, now commander of of a Special Forces battalion in Stuttgart, West Germany, said he reviewed intelligence reports on missing Vietnam servicemen while serving with a prisoner-of-war analysis unit in Seoul, Korea, from September 1983 until May 1984.

"I was shocked" by the lack of interest among military superiors about pursuing leads on live American POWs, Howard said. "I feel that a responsible estimate is that these Americans number in excess of 100."

Pentagon spokesman Robert B. Sims said he could not comment on the lawsuit but stressed that the Reagan administration is pursuing leads on live POWs and pressing Hanoi to account for missing Americans.

Howard, who won the Medal of Honor in 1971 in Vietnam, also accused two fellow officers of blowing the cover of Thai military officers, including a general, who had been providing information to the United States "concerning living American prisoners." Howard charged this "was an effort to undermine the successful intelligence-gathering activity of Special Forces Detachment-Korea on the subject of living Americans in Southeast Asia."

Sgt. 1st Class Melvin C. McIntire, with the 7th Special Forces at Fort Bragg, N.C., said he was in the analysis detachment in Korea from February 1982 to August 1984. He said he speaks two dialects of Thai, "some Laotian" and two dialects of Korean and was sent by the Defense Intelligence Agency to Southeast Asia to recruit agents who might be helpful in finding live Americans.

"My sources told me they were going to bring out two American prisoners of war in May of 1984," McIntire said. He reported this information to his superiors in Korea and then was kept from further trips to Southeast Asia and ordered back to the United States in August 1984.

"My commander was told to destroy written intelligence reports which related to the information we had gathered concerning American POWs in Southeast Asia," McIntire said in his sworn statement. "The conclusion which I reach based upon my personal experiences in Southeast Asia and in intelligence gathering on the issue of living Americans in Southeast Asia is that no one in the United States government that I have been able to talk to is interested in this subject."

He said he was interviewed by the DIA and that "all information provided was summarily explained away or discredited."

In a third affidavit, former Marine Robert Garwood, who was convicted of collaborating with the enemy in 1981, said that during the 14 years he was classified a POW, he saw American POWs. He said these sightings were in Gia Lam between 1975 and 1979, including a group of 40 getting off a railroad boxcar in 1977.

McIntire and retired Maj. Mark A. Smith, a decorated former POW in Cambodia, are the plaintiffs in the suit which asks the court to compel Reagan to take the "necessary and proper" means to obtain the release Americans held captive in Southeast Asia.

Smith in his statement said an Army major general advised him to shred the information he had written about live POWs "and forget the whole issue."