BY SUSANA HAYWARD
Knight Ridder News Service

ATOYAC de ALVAREZ, Mexico -- Yearning to know the fate of their loved ones, seven people whose relatives disappeared decades ago in Mexico's dirty war recently spent 10 days visiting an island penal colony where rumor has long said political dissidents were held.

But the trip to the Islas Marias penal facility off Mexico's Pacific coast ended last week in bitter emptiness, with no proof that their relatives were still alive.

Hearing the stories of possible torture and death left other relatives -- who didn't make the trip but gathered here to learn about it -- in tears.

''It was like searching for a needle in a haystack,'' said Georgina Landa, an official from the office of Mexico's Special Prosecutor for Social and Political Movements of the Past. 'Archives are missing. Names and crimes were obviously changed to hide the truth. Everything was mixed up. We could only look at one `dead' file, moth-eaten and dusty.''

FOUNDED IN 1905

The penal colony at Islas Marias, a three-island archipelago about 80 miles off the coast of the Mexican state of Nayarit, was founded in 1905, and there are still about 570 criminals there, serving sentences for offenses ranging from weapons and drug trafficking to homicide.

During the presidency of Luis Echeverría, from 1970 to 1976, the penitentiary held as many as 6,000 prisoners, and while most were there for common crimes, many human rights advocates think political prisoners began arriving there in 1974 as an offensive in Guerrero state by guerrilla leader Lucio Cabanas and his Army of the Poor grew in intensity.

LITTLE EVIDENCE

Investigators admit that the documentary evidence that Islas Marias housed political prisoners is fragmentary. Among the evidence was a letter tucked in a ''dead file,'' or cold case, in the national archives from jailed dissidents in Guerrero's capital, Chilpancingo, who vowed solidarity ``with political prisoners at Islas Marias, who are being tortured and killed.''

During the 10-day visit, which ended Aug. 25, Landa's group heard testimony from a handful of prisoners in their 60s and 70s, who said they remembered the arrival of captured guerrillas on the island.

One prisoner in his 70s, Francisco Rosales, said he'd spent 30 years at Islas Marias for homicide. He was released in 1974 but returned in 1978, missing four key years of the dirty war.

He and others told how political prisoners were placed in tiny cells on the seashore. At night the tide rose, and when morning came, they had drowned.

There was no way to confirm Rosales' testimony.

The visitors also said they were told of prisoners being put in cells without roofs and kept there for weeks, fed only bread and water. They heard of inmates hung by their arms from palm trees.

'STEPPING ON GRAVES'

''It was unbelievable. I didn't know if we were stepping on their graves,'' Tita Radilla, the vice president of the National Association of Disappeared People, said. "I'd look out to the sea and think how they drowned. They were kidnapped by the government, and they didn't leave proof behind.''

Some visitors complained about restrictions in their search for evidence.

''Authorities didn't want to show us a box with dozens of documents, and there are no files from 1970 to 1979. They simply said they didn't exist,'' said Antonio Iturio, 42.

''I have information my uncle was there in 1976. We know nothing since then,'' Iturio said.

"Another man in his cell got out. My uncle asked him to call my relatives and let them know he was alive at Islas Marias.''