The Arab League condemned South Yemen in strong terms yesterday for the "evil crime" of murdering North Yemen's president, Lt. Col. Ahmed Ghashmi, a week ago.

Meeting in emergency session, the Arab foreign ministers stopped short of granting North Yemen's request to expel South Yemen from the Arab League, which would have required a unanimous vote. But they imposed unprecedented sanctions that reflected their distaste for the way South Yemen's Marxist rulers conduct their affairs.

The 16 Arab states at the meeting agreed to freeze their diplomatic and political relations with South Yemen and to halt all economic, technical and cultural assistance to the impoverished country. South Yemen and six other members did not attend.

The deputy secretary general of the Arab League, Sayed Nofal, read in public a communique in which the participants said they "strongly denounced the evil crime," of Ghashmi's assassination and "condemn all who planned or executed it."

An Arab diplomat who took part in the talks said the outcome of the meeting showed that the Arab states accepted North Yemen's allegation that South Yemen was responsible for the murder and wanted to show South Yemen that they rejected "killing as an exercise of foreign policy."

Within 48 hours of Ghashmi's death South Yemen's president was deposed and killed in a leftist palace coup.

According to the Arab League communique. South Yemen was guilty of a "horrible crime which conflicts with divine teachings," and violated Article Eight of the league's charter. That article requires each member to respect the others' systems of government and " to abstain from any action calculated to change established systems of government."

North yemen's foreign minister, Abudllah Asnaj, who presented his country's case, thanked the league for what he called a "wise decision."

The league's action against South Yemen apparently is the strongest by any regional grouping of nations against a member since the Organization of American States severed relations with Cuba in 1964. The expression "freeze," also used by the Arab rejectionist states when they condemned Egyptian President Anwar Sadat's peace initiative, is not a formal break in relations, although it amounts to the same thing.

The resolution is not binding on the league members that boycotted the meeting. Aside from the small African state of Djibouti, which has good relations with both Yemens and cannot afford a break with either, those that stayed away more or less share South Yemen's radical more pro-Soviet alignment - Libya, Syria, Iraq, Algeria and the Palestine Liberation Organization. South Yemen did not appear in its own defense.

Those members presumable will maintain normal relations with the Aden government, the only avowedly Marxist one in the Arab world. The Arab League action apparently means an end to the infusions of cash from Saudi Arabia and the United Arab Emirates that South Yemen's late president, Salem Robayi Ali, accepted in an attempt to shore up his country's economy. The pragmatism that led him to accept money from Saudi Arabia and to agree to receive a delegation from the United States is believed to have been the reason his hard-line, doctrinaire associates wanted to get rid of him.

According to information presented at the Arab League meeting and accepted as true by the delegates, Robayi Ali telephoned Ghashmi on June 23 and said he wanted to send a personal envoy to the North Yemeni capital of Sanaa to discuss an urgent matter. Ghashmi, in power only since the assassination of his predecessor last October, agreed to receive the envoy.

When the envoy arrived the next morning, he was shown into Ghashmi's office. As he opened his brief-case, it exploded killing both him and the president. Reports presented to the Arab League alleged that Robayi Ali's rivals, who wanted Ghashmi slain as a pretext for deposing their own president, had switched brief-cases.