Guyanese and U.S. investigators who supposedly combed Jonestown in the days after the mass suicide-murder here overlooked until today a Peoples Temple organization chart that may prove to be of key importance to criminal investigations now under way in both countries.

The chart, which has on it the names of those Peoples Temple members who served in top positions at the time of the Nov. 18 suicide-murder, was found here this afternoon.

The chart was in the same place-at the side of the central pavilion where more than 900 of the Rev. Jim Jones' followers later died of cyanide poisoning-as when Rep. Leo J. Ryan and his party entered Jonestown Nov. 17.

The chart was considered important by members of the Jonestown hierarchy, who stopped me from copying the names on the chart that night. Guyanese police prevented reporters who found the chart today from copying the names once the police realized the potential value of the information.

In addition to providing a picture of how Jonestown was organized, the chart contains the names of persons who had top positions at Jonestown - at least serveal of whom, including Jones' son Steve and Lee Ingram, were outside Jonestown at the time of the mass suicide-murder.

Guyanese autorities have yet to release Steve Jones, Ingram and more than 20 other Peoples Temple members who were either here in Georgetown when the mass suicide ritual was occurring at Jonestown, or who managed to leave. The rest died of the cyanide potion except Jones and one of his mistresses, who died of bullet wounds.

Police here are known to be investigating the possibility that at least some of those Peoples Temple members still alive may have engaged in criminal activity before or during the death ritual.

In addition, a federal grand jury in San Francisco is now hearing evidence in an effort to determine whether a conspiracy existed that led to Ryan's death shortly after he left Jonestown on Nov. 18.

The federal grand jury in California is also looking into reports that the Rev. Jones drew up a "hit list" of Peoples Temple enemies that some of his top lieutenants and most loyal followers might intend to implement in the United States.

Guyanese police said the organization chart found today will be entered into evidence as part of an inquest now being held to determine the causes of death of those at Jonestown. Once this hearing is concluded, death certificates for the more than 900 dead Peoples Temple members can be issued in the United States.

A U.S. diplomat who was at Jonestown today when the chart was found said that the embassy in Guyana will probably request the chart-or at least the information contained on it-for use by the FBI and the San Francisco grand jury.

The Guyanese government inquest, in its second day, is being held in Matthews Ridge, a small settlement about 35 miles from Jonestown. The only testimony heard at today's session was from Odell Rhodes, who witnessed about 20 minutes of the suicide-murder rite before volunteering to find a stethoscope and then hiding, escaping death.

Rhodes testified that he and several others knew about had expressed a desire to leave Jonestown during the months preceding Ryan's visit. Rhodes said that anyone who wanted to leave was punished, either by being given extra work or by being beaten.

Rhodes testified that all mail into and out of Jonestown was censored by a four-member committee and that, beginning last September, five armed guards patrolled the Jonestown commune every night to prevent defection.