DAMASCUS, Syria (AP) _ Ali Nasser Mohammed, who vanished from the public eye after he was ousted as president of South Yemen last January, surfaced in Damascus on Sunday, one day after his supporters went on trial back home.

Speaking in an interview with The Associated Press at the government guest house where he was staying, Mohammed said Syria was working to heal divisions between Marxist factions in his country.

In another sign of possible Syrian involvement in mediating between the factions, South Yemeni President Heider al-Attas met Saturday with President Hafez Assad in Damascus. There was no word on what they discussed.

Al-Attas and Mohammed did not meet. Al-Attas left for Algeria on Sunday but his plane was diverted by bad weather and landed in Tunisia.

South Yemen, a nation of 2.5 million people, has been run by the Socialist Party since 1967, following the civil war that ended with the division of Yemen. North Yemen has a Western-oriented government.

The South Yemeni capital of Aden was torn by 12 days of violence in January between factions led by al-Attas and Mohammed, which diplomatic observers said left more than 10,000 dead.

Mohammed's group, though Marxist, was known for its willingness to seek economic and other help from the West, while al-Attas and his supporters were more rigidly aligned with Moscow.

A preliminary hearing was held in Aden on Saturday at the start of the trial of figures associated with Mohammed's faction, but neither the number of defendants nor the charges they faced could be determined.

Mohammed said 150 people were being tried, including himself in abstentia, but this could not be confirmed.

''By starting the trials, the ruling group in Aden is blocking the way of all the efforts of our friends and brothers to reach a political solution to the crisis'' in South Yemen, Mohammed said.

''It is my personal conviction that the present leadership in Aden has already decided on the sentences, and the trials are only a fiction.''

Since his disappearance following the outbreak of fighting Jan. 12, Mohammed has been reported to be in Addis Ababa, Ethiopia; San'a, North Yemen; and Damascus.

Asked to give details of his whereabouts since leaving Aden, Mohammed declined comment. Several newspapers in the Persian Gulf have published interviews of him since his ouster, but none said where the interviews were conducted.

Syrian officials and news media have never disclosed Mohammed's presence in Damascus.

Mohammed, 46, was deposed at a meeting of the ruling Socialist Party Central Committee, after the faction led by al-Attas took control of the capital.

Referring to the Syrian mediation effort, Mohammed said, ''Unless the rulers in Aden accept the mediation efforts of our brothers and friends, the unity of Democratic Yemen will be in great danger.''

Arab diplomats in Damascus privately expressed their doubts as to a possible reconciliation between the two factions.