Mark Lane, the well-Known conspiracy lawyer who represented the Peoples Temple and the Rev. Jim Jones, knew a great deal more than he was willing to let on about the explosive situation at Jonestown and felt something was very wrong there long before Rep. Leo J. Ryan (D-Calif.) arrived Nov. 17.

During an airborne interview as he flew with the congressman and his party toward the remote agricultural commune last week. Lane said that "maybe 10 percent of the people at Jonestown want to leave."

Lane, however, insisted that nothing more than "peer pressure" was being used to keep people there against their will. Lane generally portrayed Jones and his followers as the victims of unfair publicity and a possible conspiracy on the part of various U.S. government agencies, such as the Internal Revenue Service and the Social Security Administration, to destroy the socialist Peoples Temple commune in Guyana's rain forest.

Last week, Lane was intent upon demonstrating to Ryan and nine journalists who accompanied the congressman to Jonestown that it was, for the most part, exactly what its supporters claimed: an unusual, interracial socialist community where more than 300 of Jones' followers were living peacefully, receiving all the food, medical attention and liberty they needed.

But this week, after Ryan and four others were killed in a hail of bullets fired by Jonestown gunmen and after Jones led 408 of his followers in a mass suicide-murder that stunned much of the world. Lane admitted he knew far more about the real conditions at Jonestown than he was ready or willing to acknowledge before the violent tragedy occurred last weekend.

For example, Lane says now that he knew strong depressants and tranquilizers were used to keep the people at Jonestown against their will. He also knew that alleged practice suicide drills had in fact taken place.

Lane also says he was warned beforehand that the grilled cheese sandwiches served on Saturday by the Peoples Temple to Ryan and others in his party may have been laced with tranquilizers or other drugs.

But instead of warning anyone of that possibility, Lane said later that he simply did not eat the sandwiches.

"I brought along some cough drops, which have a lot of sugar in them," Lane said. "I sure as hell wasn't going to eat the cheese sandwiches."

Lane claims now that he warned Ryan, before the congressman and his party left here for Jonestown, that Jones was sick and that the visit could have explosive consequences. But given the adversary relationship between Lane and the congressman, who thought Lane was trying to stall or prevent the trip, the warning, if it was made, was apparently dismissed.

Lane did not tell anyone else who traveled with Ryan that Jones was unstable and that Jonestown was in many ways a prison camp possibly on the verge of being destroyed by its leader.

Lane says he knew Jones was serious about taking his followers to their deaths. He says he now believes Jones sketched out a plot that included having trained marksmen kill "enemies" of the Peoples Temple once the mass suicide-murder occurred.

Lane's knowledge beforehand of much of the reality of Jonestown and his willingness to talk about it only now - after at least 414 people are dead - has infuriated at least one of the "concerned relatives" who was on the fateful fact-finding mission.

This relative, who asked that his name not be revealed because he, too, believes that some of Jones' followers will attempt to kill those they see as enemies of the Peoples Temple, said Lane's failure to disclose what he knew beforehand constitutes "complicity in the crime."

"I find it incredible," this relative said, "that what happened at Jonestown is being called a mass suicide. Babies and children whose mothers give them cyanide have not committed suicide. They have been murdered." He said Lane possibly could have prevented the tragedy had he spoken out.

Lane countered this accusation by saying that the concerned relatives knew far more about the real conditions at Jonestown than he did. When it was pointed out that it was the concerned relatives who tried to bring their fears and beliefs to public attention - while Jones and his attorneys tried to discredit them - Lane said that "if they [the concerned relatives] weren't crazy, they wouldn't have been discredited."

Lane also said it was his belief that the FBI and the CIA had agents in the Jonestown complex and that the U.S. government was as much aware of the situation there as he was. Asked for his evidence, Lane said: "I don't have proof but I have strong beliefs."

In justifying his silence about much of what he knew beforehand, Lane has also said he believes that exposing the real situation would have done little good. It might, he now argues, have precipitated earlier a mass suicide-murder such as the one that occured after the Ryan visit.

"What could have been done?" Lane asked. "I believe that if the Marines had been called in, 90 percent of the people at Jonestown would have fought to their deaths. It was a hard life, he [Jones] was a dictator but the people there didn't want to go back to the United States. They wanted to go to the Soviet Union."

Lane said he hoped before Ryan's visit that the congressman would have learned enough to publicize deficiencies at Jonestown and that Jones might have instituted "reforms."

Instead, the visit apparently triggered Jones to order trained marksmen to kill as many of those traveling with Ryan as the gunmen could before Jones ordered a real "white night," his code name for the suicide-murder plan he had talked about - and faked - so many times before.

For his part, Charles E. Garry, who served as general counsel to the Peoples Temple, has continued to maintain that he thinks, even after last weekend's tragedy, that Jonestown was "a beautiful thing" and that Jones did not stop people who wanted to leave the remote commune.

Lane was brought in only recently to investigate the possibility of filing a conspiracy suit against U.S. government agencies that Jones believed were, along with a number of California publications and former Temple members, trying to destroy both Jones and Jonestown.

Lane, who along with Garry was at Jonestown when Jones began ordering his people to take the mixture of Kool-Aid and cyanide that killed them, managed to talk an armed guard to allow himself and Garry to escape.

They walked the five miles into nearby Port Kaituma and were brought out of the area on Sunday. Lone is now back at his area on Sunday. Lane is now back at his Memphis, Tenn., home, where he has said he may write a book about his experience.

Is it not entirely clear whether Lane and Garry are still lawyers for the Peoples Temple, which, despite the events of last weekend, still has thousands of adherents in the San Francisco area as well as at least 45 members now under house arrest here in Guyana.