It was around midday on Feb. 3, 1971, when U.S. Air Force Lt. Col. Robert Standerwick bailed out of his F4 Phantom jet while flying a reconnaissance mission over the Ho Chi Minh Trail in eastern Laos.

According to U.S. Embassy records here, Standerwick was known to be alive on the ground in heavy jungle south of the Mugia Pass when his copilot, Maj. Norbert Gotner, who had also ejected safely, heard gunfire in the area.

"I'm hit, I'm hit," Standerwick radioed to his wingman flying overhead. "I'm going to give up." Gotner was captured by Vietnamese troops, imprisoned for two years and released. But that was the last ever heard from Standerwick, one of nearly 2,500 U.S. servicemen listed by the Pentagon as missing in Indochina and presumed dead.

Now, 12 years later, Standerwick's daughter, Lynn, 25, and another American, U.S. Special Forces veteran, Lance Edward Trimmer, 43, are under investigation in northeastern Thailand for involvement in illegal forays led by retired Special Forces officer and Vietnam war hero James G. (Bo) Gritz to search for American prisoners of war who he believes are still alive in Laos.

Trimmer and Standerwick were arrested Feb. 13 at a rented house in the town of Nakhon Phanom in northeastern Thailand just across the Mekong River from Laos. They were jailed for two days and charged with possession of an unlicensed radio transmitter, an offense punishable by a five-year jail term. Also found in the house were fatigues, scuba diving equipment, jungle knives, cartridge belts and a gas mask.

The two Americans, now free on bail, rejected the charges and denied involvement in Gritz's rescue efforts. But a former Gritz associate who says he participated in Operation Lazarus, an unsuccessful Hollywood-financed raid into Laos in November, has said Trimmer and Standerwick were involved in communications support for Gritz's operations.

Their presence in Nakhon Phanom has fueled speculation that the 44-year-old former Green Beret lieutenant colonel, the Oklahoma-born son of a bomber pilot killed in World War II, may have launched another foray into Laos with another group of American veterans.

The Los Angeles Times reported Monday that it had received a 12-page handwritten letter from Gritz saying he and two other Americans are in Laos on a new rescue mission. The letter, carried out of Laos by a runner, said Gritz had found "some POW ID" but did not describe it.

The Times quoted the letter, which was dated Feb. 12, as saying both the Central Intelligence Agency and Defense Intelligence Agency were aware of Gritz's plans. Spokesmen for both agencies denied Gritz's allegations to the Times.

The Thai police Special Branch has stepped up a search for Gritz in Thailand, and both Vietnamese troops and forces of the Communist Pathet Lao government in Vientiane are reported to be hunting him and his men in the jungles of Laos.

The episode and the tangled tale surrounding it illustrate the powerful emotions that still color the issue of prisoners-of-war and servicemen missing-in-action 10 years after the last American combat troops withdrew from Vietnam. But they also serve to crack open a window on Thailand's murky underworld of foreign mercenaries, private army-resistance groups and intelligence operatives who often are united only by their opposition to the Communist governments in Indochina.

Gritz, his associates and their activities also raise questions about top U.S. government officials' role in and attitude toward his private POW rescue operations. The government has denied any involvement in Operation Lazarus, saying it neither supports nor condones such actions and considers them "very unhelpful" to official efforts to resolve POW-MIA issues. The Justice Department has said it has the case "under review."

However, a participant in Operation Lazarus, former Special Forces sergeant Charles Patterson of Dinuba, Calif., has said that President Reagan was told about the operation and gave it his tacit blessing at a meeting set up by actor Clint Eastwood at Reagan's California ranch.

A White House spokeswoman in Washington said she had "no knowledge of such a meeting" and added that the government does not "support or condone cross-border forays which serve to jeopardize" other efforts to obtain information about possible American captives in Indochina. She said people "involved" in such efforts "have been so informed."

An "operations plan," purportedly written by Gritz, says it was assumed that "the U.S. government cannot commit official assets until positive proof of U.S. POW presence is provided," but that "once such a determination has been made the U.S.G. will follow the president's stated policy to do whatever is required to return the POWs to U.S. control."

It added, "It is hoped that the U.S.G. will also continue to provide clandestine support to those dedicated indigenous groups that made the liberation possible."

"It is time the POWs came home," it concluded. "I intend to do everything I can to cooperate and coordinate this effort with executive desires. It just needs to be finished and if I and my people don't do it, I don't know anyone in Washington who will.

"It takes action and both Teddy Roosevelt and John Wayne are dead. Hopefully, like the name of this operation, their spirit and resolve live today in the heart of our president, resurrected as those declared dead by our system soon will be."

The document, entitled "Intelligence Summary and Situation Report: Operation Lazarus," was signed by Gritz as "commander" of the operation. It was dated Nov. 27, 1982, the day he reportedly launched the foray into Laos that was to end in fiasco.

According to knowledgeable sources in Bangkok, Patterson gave a copy of the plan to Soldier of Fortune, the American magazine for mercenaries, and it later found its way to the English-language Bangkok Post newspaper, which broke the story of Operation Lazarus on Jan. 31.

Patterson also gave an extensive interview to Soldier of Fortune--a summary of which was obtained here--in which he named Eastwood and a Litton Industries executive identified as Jim Wijinksky as major backers of Operation Lazarus. He said that in August last year he and Gritz flew to Eastwood's California ranch for a meeting with the actor and his manager, Fritz Mann. There, Patterson said, Eastwood pledged $30,000 for the operation in return for book and movie rights and promised he could put Gritz in direct contact with President Reagan.

Patterson, said the Litton executive contributed eight advanced Individual Data Transmission units, worth about $50,000 apiece, to enable the group to send messages via coded, high-speed transmissions in bursts of six seconds.

Patterson, who is also a former Green Beret, said that another Gritz accomplice, Gordon Wilson, told him Eastwood had arranged a meeting with Reagan at the president's ranch in early December in which Operation Lazarus was discussed. According to Patterson, Wilson sent a radio message to Trimmer in Nakhon Phanom quoting Reagan as saying that if Gritz's team brought back one live POW, he would "start World War III to get the rest."

In a speech to relatives of missing Americans last month, Reagan pledged to "take decisive action over sighting reports that can be confirmed." He added, "I am sure you understand that some of these approaches must be done quietly."

In preparing for previous attempts--also unsuccessful--to rescue POWs in Laos, Gritz has claimed to have had access to top-secret intelligence data from American reconnaissance planes, satellites and agents, as well as from his own Laotian resistance sources.

In his letter to the Los Angeles Times, he said he had "12 CIA-DIA generated targets which . . . could hold POWs."

In an interview in the March 1982 edition of Penthouse magazine conducted by Boston Globe reporter Ben Bradlee Jr., Gritz said a Pentagon superior had asked in 1979 if he would consider early retirement to undertake a POW rescue mission as a private citizen. He said he spent the next 30 months preparing for the operation until March 1981 when he was asked to call it off because of a Reagan administration attempt scheduled for April.

That operation, involving anticommunist Laotian mercenaries organized by the Central Intelligence Agency, proved fruitless. The Washington Post reported in May 1981 that the force had found no evidence to support intelligence reports that a group of American POWs was still being held in Laos.

In a Boston Globe article, Bradlee quoted Gritz as saying that he had been contacted again later, in June 1981, about the POW situation by a secret military intelligence agency created after the abortive April 1980 attempt to rescue the American hostages in Iran. Gritz would not identify the agency.

According to sources here, however, the agency is a small elite intelligence and operational unit under the Defense Department. The sources described it as an offshoot of the Blue Light unit formed for the Iran rescue mission and said it has been given charge of all covert MIA-POW operations.

Despite Gritz's zeal and what he claimed was careful planning based on sound intelligence, last year's Operation Lazarus ended in failure with tragicomic episodes at times approaching slapstick.

"It's a good day to die," Gritz was quoted as saying dramatically as he and his men prepared to cross the Mekong at 9 p.m. on Nov. 27. Gritz and Patterson were accompanied by two other Americans, Gary Goldman and Dominic Zappone, and 15 Laotian resistance fighters.

The target of Operation Lazarus, according to Gritz's plan, was the Xepon area of eastern Laos allegedly containing three closely positioned POW detention sites. Gritz claimed that one camp at Phu Xun mountain held 80 Americans, a second held 35 and a third had five POWs.

After trekking through the jungle for three days, Patterson said, the group was ambushed by Laotians later identified as belonging to another anticommunist resistance group. Gritz, Goldman and Patterson abandoned their equipment and fled, and Zappone was captured, according to Patterson. He said one Laotian was killed and three wounded.

Heading back to Thailand, the group passed too close to a village on Dec. 3 and was chased by dogs and Pathet Lao soldiers to the Mekong. Gritz and his men hit the river on the run while stripping off their clothes, according to Patterson. The group became separated on the other side, and Gritz ended up having to take a bus back to Nakhon Phanom in his underwear, telling the driver he was an oil worker and had accidentally fallen in the river.

In his letter to the Los Angeles Times, Gritz said Patterson "was the only one to fling his boots, uniform and equipment aside before plunging into the Mekong--in his underwear."

Determined to find Zappone and the lost equipment, Gritz led another team back into Laos on the night of Dec. 9 as Patterson headed back to Bangkok. There Patterson said he met Gordon Wilson, who, initially unaware that the mission had failed, reported Reagan's alleged tacit support for the operation.

But when Patterson went to the U.S. Embassy for help in getting his visa renewed, he was stiffly upbraided by embassy officials. They refused to help on grounds it would amount to condoning the Laos operation and warned him he could be tried for violating the Neutrality Act. Patterson went home later that month.

Gritz reportedly emerged from Laos again around Christmas, but without Zappone. In an interview with the Los Angeles Times after returning to the United States in January, Gritz said Zappone had stayed in Laos to maintain contact with friendly forces and crossed into Thailand shortly after Jan. 1.

However, according to informed sources here, Zappone was ransomed for about $17,500 and 40 boxes of medicine in a trade believed to have been arranged by U.S. agents.

Now the Gritz legend is a subject of controversy and debate among friends and Vietnam hands here. Supporters continue to view him as a dedicated man with a mission. But others see him as an adventurer living in the past or an exploiter of the families of missing servicemen.

According to one western diplomat, Gritz has obtained money from the families in the past for his operations, which the source called "amateurish" and based on "appalling intelligence."

A U.S. officer who said he knew Gritz in Vietnam in 1967 called him a "real hero" who deserved his numerous war medals for leading indigenous troops in a special mobile guerrilla force more than 100 times behind enemy lines.

"He wasn't a loony by any means," the officer said. "But I just don't know what to make of him now. It's unfortunate that a guy with a well-deserved reputation is selling it to a certain extent. Maybe he couldn't adjust to peace."