"I opened a heavy iron door, shined in the flashlight, and what I saw froze my blood. Before me was a room of approximately one meter square, completely dark; a true dungeon with walls and ceilings covered with cockroaches."

That description is contained in a memorandum obtained by The Washington Post along with an unpublished international report on human rights violations allegedly committed by the government of El Salvador.

The report, written after an on-site investigation last year by the Organization of American States' Human Rights Commission, concludes that government security and paramilitary organizations in El Salvador are responsible for the deaths of "numerous persons," as well as for acts of physical and psychological torture and inhuman imprisonment in secret dungeons.

The report, which is to be made public along with a series of proposed resolutions in March, also accuses the Salvadoran government of "systematically persecuting" the Roman Catholic Church and of abusing political opponents.

At least four priests have been slain there in unsolved crimes over the past two years, the most recent last Friday when the Rev. Octavio Ortiz was machinegunned, along with four other persons, in a parish hall meeting. According to the government all the priests had been active in organizing peasant union groups that the government has banned.

Roman Catholic Archbishop Oscar Arnulfo Romero yesterday ordered cancellation of all church services in El Salvador for three days in mourning for the priest killed Friday and said all those involved in the killing were excommunicated from the church.

The report itself charges the government with maintaining secret detention centers and their discovery by human rights commission investigators is detailed in the internal memorandum written soon after the investigation nearly a year ago.

Following an uneventful visit to the headquarters of the National Guard in San Salvador, the memorandum said, two OAS investigators returned there several days later with a clandestinely obtained map of the third floor of the building.

Accompanied by the then head of the National Guard, Gen. Ramon Alvarenga, who was acting under government instructions to assist them, the investigators climbed a set of back stairs and found what appeared to be a torture room.

According to the memorandum, the investigators "recognized it as the interrogation room described [on the map]. This room had a table with electrical apparatus on top of it and what was apparently a two-way mirror."

When questioned, the general said the room was used for photography, although the military photographer present later denied such usage.

Noting that "the atmosphere grew cold" in their meeting with Alvarenga, the investigators said they then indicated another closed door whose entrance was blocked with a pile of old tires.

"We started to remove them," the memorandum said. "At first, no one helped us. But after seeing our determination, Gen. Alvarenga said dryly, 'Help them,'" to nearby soldiers.

That room, a two-meter -- about 6 1/2 feet -- square cell, led to another passageway with the doorway blocked by at least 15 metal cots of the type former prisoners have said are used to chain detainees in a spread-eagle position.

It was behind that door, the memorandum said, that the investigators found at least four of the windowless, cockroach-infested "dungeons," with initials scratched in the metal doors.

The initials, they said, were the same as those of five persons whose disappearance over the past three years has been charged to, and denied by, the government.

Again questioned, the memorandum said, Gen. Alvarenga said the initials could have been carved by "an enemy of the government."

The current president of El Salvador, Gen. Humberto Romero, was elected in Februrary 1977 in what was widely alleged to have been a government-directed electoral fraud.

The military has held the presidency for the past 46 years, supported by the small landed and industrial oligarchy that controls the majority of the wealth of the nation, smaller than Maryland and with a population of 4.5 million.

Both Romero's and the previous military governments have been accused by domestic and international human rights organizations of widespread repression against the political opposition, the church and peasant groups that it charges are part of a guerrilla-led communist conspiracy.

The OAS report recommends the dissolution of Orden, an 80,000-strong paramilitary organization that serves as a government spy network in cities and villages throughout the country.

While it notes that the laws of El Salvador make reference to due legal process, "in practice the legal resources are not sufficient to protect those persons arbitrarily deprived of their fundamental human rights."

The report said at least 99 persons who have disappeared are believed dead or held in the secret detention centers

The Human Rights Commission visit to El Salvador resulted from an invitation issued in September 1977 by the Romero government. The invitation was cited by the State Department as positive human rights progress when the U.S. government approved a previously withheld $90 million loan to El Salvador.

The report was transmitted to the El Salvador government for comment in November. The government has been given until Feb. 28 to respond.