Communist leader Todor Zhivkov promised "radical transformations" of economic policy here today at a Bulgarian party congress that is also expected to consolidate moderate changes in political leadership under pressure from Soviet party chief Mikhail Gorbachev.

Zhivkov, whose close relations with Moscow have been strained since Gorbachev took power last year, said Bulgaria would decentralize management, toughen discipline and link workers' pay to performance in economic reforms potentially more dramatic than those planned by Gorbachev for the Soviet Union.

However, the 74-year-old leader also indicated his intention to extend his 31-year tenure as Communist Party secretary general and limit a shake-up of top officials he has overseen in the last two months. Zhivkov has been seen as the East European party leader most likely to be forced out of power under Gorbachev.

The speech and a low-key atmosphere at the congress, which followed the first Soviet party congress under Gorbachev, suggested that Bulgaria, the Soviet ally most affected so far by Gorbachev's new leadership, would avoid further upheaval this week.

"There is certainly pressure from the Soviets, and the Bulgarians know it," said one western diplomat. "But the Soviets can't run this country."

Zhivkov appeared to begin a shift of course in the months before the congress by launching a purge of party organizations and making four changes in the ruling Politburo. These moves were followed by a major government reorganization involving the abolition of six ministries, the naming of a new prime minister and the shift of other top government officials.

In Sofia, home of more than a tenth of Bulgaria's 9 million people, the top party official was dismissed, about three dozen members were expelled from the party and more than 100 were reprimanded. Most of those disciplined were managers tied to failures in transportation, communications and housing or reported cases of corruption, according to diplomats.

The changes have marked a sharp break in Bulgaria's steady record as one of the fastest-growing and most favored of Soviet political allies. After relying for years on such benefits as large, subsidized Soviet oil supplies and the rapid industrialization of a once agrarian nation, Bulgaria was stricken when cutbacks in Soviet oil combined with a severe drought and increasing management failures in industry.

Public signs of Moscow's displeasure reached a peak last October when Gorbachev, during his first visit to Sofia as Soviet leader, pointedly noted that his discussions with Zhivkov had included "ways to cope with the existing difficulties" and were carried out "without shunning the sharp edges."

Diplomats here said the flurry of subsequent changes was in part meant as a response to the Soviet pressure. However, they said, Zhivkov did not yet appear ready to take major steps to renovate the leadership ranks and it remained unclear how far the announced economic reforms would go.

"They realized they had to do something -- the Soviets were breathing down their necks -- and this is what they came up with," said one skeptical western expert. "But it remains to be seen whether this will amount to more than the tinkering that has been going on here for years."

Expectations that additional political changes may be slow and tightly controlled have been strengthened by indications from Bulgarian sources that no further high-level personnel shifts will be made during this week's congress, which is due to end Saturday.

At the same time, the head of the Soviet delegation here, Prime Minister Nikolai Ryzhkov, offered a positive assessment of the party's progress in a speech this afternoon.

"The line pursued by the Bulgarian party has strongly united the Bulgarian nation," Ryzhkov said. "In the Bulgarian comrades we see loyal and reliable friends."

In reorganizing the party and government, Zhivkov promoted several young technocrats thought to be possible successors as party leader, including Chudomir Aleksandrov, 49, the new secretary of party organization, and Ognyan Doinev, 50, the chief of a powerful new council governing economic policy.

Diplomats noted, however, that the veteran leader had skillfully prevented any of the younger leaders from assuming a preeminent position, and had kept a dominating group of close followers, including seven men over 70, in the Politburo.

Concrete moves toward economc change have included the sanctioning of a new labor code that loosens controls over hiring, firing and wages and gives factories a greater voice in their affairs under a "self-management" system. The economic bureaucracy has been reorganized so individual firms will be grouped into conglomerates that will report directly to a streamlined economic council.

Zhivkov said today that under a program now being prepared, self-government organizations in factories would make independent decisions about planning, production, trade and research rather than being bound by detailed plans drawn up by ministries.