Algeria's acting chief, Col. Benjedid Chadli, was named today to succeed the late president Houari Boumediene in a transition apparently avoiding a disruptive power struggle.

The appointment of Chadli, 49, considered a political moderate, was a defeat for the left wing of the Algerian leadership eager to intensify Boumediene's push for rapid social and economic change.

Chadli was named both secretary general of the ruling National Liberation Front and sole candidate for the Feb. 7 presidential election -- with victory assured.

The 3,269 delegates to the party congress included more than 600 army officers who helped to brush aside the favorite of the left, party functionary Mohammed Salah Yahiaoui. It had been thought that Yahiaoui might win the top party post, if not the presidency, but the convention concentrated both top positions in the hands of Chadli.

Still, it is thought that Chadli will have to consolidate power, now dispersed within the ruling party, in order to wield the powers that Boumediene did.

Thus no startling policy changes were thought likely in the immediate future but diplomatic sources said they expected a gradual "mellowing" of Boumediene's anti-Western, anticapitalist stance.

Yahiaoui is also a member of the council, but at the left end of the spectrum. He preaches Islamic and revolutionary purity and was known as a faithful follower of the ascetic Boumediene -- who died Dec. 27 after a lengthy hospitalization for a blood disease.

The Algerian leadership, drawn from the army, party, Cabinet, National Assembly and "mass organizations," stressed the need for an orderly transition and the army played a preponderant role.

This made it likely that the leader would come from the army, the more so since a conflict with Morocco over the Western Sahara has fostered a preoccupation with national security.

The party congress, conducting all its important business behind closed doors, elected a 17-member Politburo with Yahiaoui as the only prominent leftist. Virtually all the other Politburo members, including Chadli and Foreign Minister Abdelaziz Bouteflika, were regarded as moderates.

The Politburo will surpervise Algerian foreign and domestic policies for the next five years, and its composition was regarded as another victory for the moderate Algerian leadership.

Chadli, in his first statement as presidential nominee, pledged to "follow the path of the late president Boumediene to strengthen the irreversible adoption of the socialist system and preserve our national independence in its widest sense."

Chadli's brief speech contrasted with a three-hour monologue delivered by Yahiaoui at the opening session Saturday. Leftist and revolutionary slogans were chanted today by small groups among the delegates, but it was not clear whether the slogans were a demonstration for or against the presidential nominee.

Chadli, dressed in an elegantly tailored pin-stripe suit, calmly glanced at the shouting groups but displayed no other reaction.