PRAGUE, FEB. 25 -- As a wet snowfall pelted the Old Town Square here today, new Communist Party leader Milos Jakes stood before a crowd assembled to celebrate the 40th anniversary of the party's full rule and repeated his promise of "the restructuring of all spheres of social life."

The address, Jakes' most important public appearance since he became party leader in December, was intended to crown a mass rally reminiscent of the demonstration that preceded the Communist takeover of Feb. 25, 1948. Yet even as the new leader spoke, the audience of several thousand factory workers, military conscripts and party activists streamed out of the square, having remained only long enough to hear the national anthem.

By the time Jakes had finished, the historic cobblestone quadrangle was more than half-empty, and the gala anniversary celebration was abruptly cut short. Thirty minutes after arriving, Jakes, President Gustav Husak, the former party leader, and the rest of the top Communist leadership filed off the back of their specially built podium, unapplauded by those remaining.

The meager public display, which came after weeks of anniversary-linked propaganda in the state-controlled media, strengthened recent indications that there is a widespread public mood of apathy and disenchantment with Jakes here only two months after he took power.

The 66-year-old leader, who built a career as a colorless, occasionally ruthless party bureaucrat before succeeding Husak, has publicly committed himself to speeding up Czechoslovakia's cautious imitation of recent Soviet economic reforms.

But Jakes' clearest message to Czechoslovaks has been his repeated, sometimes angry, insistence that no reconsideration of the liberalizations of the 1968 "Prague Spring" is possible under his rule.

"In 1968," he said today, "the revolutionary achievements of the victorious February {1948} and our alliance with the Soviet Union and other socialist states were threatened. Such is the historical truth and nothing substantial can be changed in it."

Such statements and a continuing hard-line government policy toward opposition groups has led many Czechoslovaks to conclude that Jakes intends to defend rather than modify the orthodox Stalinist political order that has prevailed here since the 1968 Soviet-led invasion, with economic alterations tailored to satisfy Moscow.

"If you read the official speeches now there is a clear pro-Gorbachev tendency," said Jiri Dienstbier, a prominent dissident. "But nothing happens in the realm of facts."

The emergence of Jakes' conservative line contrasts markedly with developments in neighboring Hungary and Poland, where communist leaderships facing economic crisis and popular pressure are extending the outer limits of Soviet Bloc economic and political liberalization.

While Moscow has seemed anxious to prevent political reform in Eastern Europe from going too far, there seems to be no strong Soviet pressure on Jakes to follow the policies of public openness and greater tolerance for intellectual opponents pursued by Gorbachev.

In fact, one of Jakes' first moves as party leader has been to attack expectations both at home and abroad that Moscow might reevaluate the reforms of the Prague Spring and the role of its leader, Alexander Dubcek.

"Here, as far as the {1968} crisis development is concerned, our positions are identical," Jakes told reporters after meeting Gorbachev in Moscow last month. "We have nothing to change here."

Holding the ideological line on 1968 seems to haunt Jakes' administration as the 20th anniversaries of the reform drive and invasion approach this year. Almost every major official speech now refers to the issue, and Jakes in particular seems driven to deny Dubcek's assertion, made in an interview published in the West last month, that the new policies of the Soviet Union and Czechoslovakia follow the same line as his own.

"There is a gaping difference between restructuring in the U.S.S.R. and our country, on the one hand, and the plans of the right wing at that time on the other," Jakes said in a speech to the Central Committee and government here yesterday. He went on to explicitly endorse the military intervention, a stand recently avoided in public by both Soviet and moderate Czechoslovak politicians.

The aggressive reassertion of the counterreformist order of the party has been accompanied by continued repression against the Charter 77 human rights group and independent cultural organizations. An attempt by Charter 77 to hold a discussion in a Prague restaurant last month was broken up roughly by police. Even a more modest initiative by several theaters to hold a forum on a controversial 19th-century literary figure was recently stifled by police because several blacklisted intellectuals planned to attend.

While privately acknowledging the stasis in political policy, government and party officials argue that Jakes has given new impetus to plans for economic decentralization and cuts in the bureaucracy that slowly took shape in the last year of Husak's leadership.

About one-third of state enterprises have been granted more independence from central planning authorities this year, and provisions for private enterprise in the service sector were modestly expanded this month.

Government officials say that a major reorganization of the state bureaucracy, including the elimination of one-third of its personnel, is supposed to be planned by midyear and implemented soon afterward, while a major law decentralizing economic activity is to take effect next January.

While Czechoslovak officials point out that these changes are momentous compared to the past 20 years of relative stagnancy, critics say that the party is still overseeing a slower and more modest version of Gorbachev's economic reforms in the Soviet Union, and lags a generation behind the East European neighbors with which it used to compare itself.

"There is a struggle going on," Dienstbier said. "But still, you can't find anyone in the Politburo who thinks they could survive a real reform. So they will never take the initiative."