South Yemen, the only Marxist-Leninist state in the Arab world, today became Moscow's first Arab ally to voice unequivocal support for the Soviet invasion of Afghanistan.

By contrast, the Palestine Liberation Organization was divided on the issue and such traditional Soviet allies and arms customers as Syria, Iraq, Libya and Algeria either maintained an embarrassed silence or openly condemned the intervention.

South Yemen's state-run Aden Radio broadcast a foreign ministry statement praising the Soviet action and denouncing international criticism of Moscow. The South Yemeni show of support put the radical Aden regime once again squarely at odds with its Arabian Peninsula neighbor, Saudi Arabia, which has strongly condemned the Soviet move.

Yasser Abed Rabbo, a senior official of the pro-Soviet Democratic Front for the Liberation of Palestine and a member of the Palestine Liberation Organization executive committee, voiced support of the Soviet action as "a great help to all revolutionary forces."

However, Mahmoud Labady, the chief spokesman in Beirut for PLO chief Yasser Arafat, pointedly refused comment on the issue. Arab diplomatic sources said Arafat told the Soviet ambassador to Lebanon that an overt PLO show of support could jeopardize vital PLO financial support from conservative Arab oil states.

Syria, which is heavily dependent on Soviet arms supplies, has refrained from outright criticism or support of the Soviet invasion. Algeria likewise has withheld comment.

Iraq, however, whose relations with Moscow had deteriorated over the past two years as a result of bloody purges of Iraqi communists, bitterly attacked the Soviet invasion.

"The foreign intervention in Afghanistan is a serious phenomenom that can be neither justified nor excused," Iraqi President Saddam Hussein said Sunday.

Even Muammar Qaddafi's Lybia expressed mild disapproval of the Soviet invasion.

"We do not approve of aggression by one country against another," said Abdel Ali Obeidi, general secretary of the Lybian People's Congress in a statement published here yesterday.