Guyanese authorities said today they want to question conspiracy lawyer Mark Lane about the circumstances surrounding the killings of Rep. Leo J. Ryan and four other members of his party on a remote airstrip in the heart of Guyana's rain forest.

Specifically, authorites said they believe Lane may be the only living and presumably uninvolved-Witness able to say whether the Rev. Jim Jones personally ordered the Nov. 18 attack on Ryan or whether the People's Temple gunmen acted under the direction of other members of the Jonestown hierarchy.

The ambush, which was unsuccessful in the sense that some members of the congressman's party survived, triggered Jones' decision to force his followers to take poison that left more than 900 Jonestown residents dead only hours after Ryan was killed at the Port Kaituma Landing field.

The question whether Jones or some of his aides ordered the attack could have a bearing on future prosecutions here of three of Jones' top lieutenauts, who say they were ordered to take a suitcase full of money and several letters to the Soviet Embassy in Georgetown. The three, Mike Prokes and Mike and Tim Carter, made it as far as Port Kaituma before being apprehended by Guyanese police. They are now being held in Georgetown.

Lane, one of two Peoples Temple lawyers who accompanied the Ryan party on its fateful trip to Jonestown, had remained behind after the congressman left for the airstrip with his group of aides, journalists, a U.S. Embassy aide and a Guyanese government official, as well as 16 persons who had decided to defect that day from the remote agricultural commune

Lane, who has left Guyana for his home in Memphis, Tenn., has said publicly that shortly after the Ryan party left Jonestown, Jones told him that the congressman and his group might be killed. But, at least publicly, Lane has not elaborated on whether he believes Jones ordered the ambush personally or simply knew that others from among his hierarchy had directed that the attack be carried out.

According to the senior state counseior prosecuting Larry Layton, the Jonestown loyalist charged here with murder and attempted murder in connection with the Port Kaituma ambush, Layton had denied that Jones personally ordered the killings.

Accordingly to the counselor, Mangram Kissoon, Layton has told Guyanese police that he does know why he decided to join Ryan's party as it was leaving Jonestown and then, once aboard the smaller of two-planes sent to pick up the congressman and his group, why he opened fire in the plane carrying four other defectors.

Layton was nowhere near the larger aircraft when Ryan, three newsmen and one of the 16 real defectors were sent shot by other Jonestown gunmen. He nevertheles has been charged with these murders as well.

Kissoon explained today, at the beginning of the initial inquest that will determine whether Layton will be brought to trial on the eight charges against him, that Layton was charged with the five murders under a Guyanese law that makes "aiding and abetting" a crime that same as committing the crime itself.

Layton could be hanged if the charges against him are sent to trial and he is convicted. Lane's testimony is not needed to prosecute Layton but, according to Kissoon, could be vital to determing who, if anyone, ordered Layton to carry out the actions with which he has been charged.

As far as is known, the gunmen who carried out the attack on the larger aircraft all died later when Jones ordered his followers to drink a potion of grape drink, cynaide, and tranquilizing drugs.

Prokes and the Carter brothers escaped death at the Peoples Temple by leaving with the cash and letters destined for the Soviet Embassy. The three also apparently carried with them automatic weapons for reasons that have so far remained unexplained.

Lane and Charles E. Garry, the Second Peoples Temple lawyer at Jonestown on Nov. 18, have said they also escaped death when they talked a guard into allowing them to leave before the suicide-murder rite got very far along. Lane did give a statement to Guyanese police, Kisson said, although, apparently in the confusion after the mass suicide and murder was discovered, certain important questions were not asked.

Kissoon did not explain why he is not also interested in talking to Garry about the circumstances surrounding Ryan's murder.

Kissoon said it would be impossible for Guyana to ask U.S. authorities to extradite Lane since there is no reason to believe he assisted a crime here. Lane could, however, voluntarily return for questioning or submit to questioning in the United States.

(In Washington, the State Department announced Tuesday it has cleared diplomat Richard McCoy of allegations made in notes and memorandums found in Jonestown that he had been "sexually compromised" by cult members when he was a U.S. consular officer in Guyana, United Press International reported.)