MOSCOW, JULY 2 -- What a difference 4 1/2 years makes.

When Mikhail Gorbachev opened the last Soviet Communist Party congress in February 1986, he held the 5,000 delegates spellbound for more than five hours describing his plans for reform.

More than two dozen times the Palace of Congresses vibrated with applause. When he had finished, the delegates rose to their feet as one and let loose a tumult of cheering and clapping that went on for more than 10 minutes. By all accounts, the 27th Party Congress -- the new leader's debut before the Communist faithful -- was a politician's dream.

Today's opening of the 28th party congress presented a far different vision of the Soviet leader's prospects and of the forces of change he has unleashed since that last national party gathering. It took two hours of bickering before Gorbachev could begin his keynote speech. And during the commotion, one delegate grabbed the microphone to demand that the current leadership not be allowed to preside over the congress.

When Gorbachev finally spoke, applause was no more than polite, even as he appealed for party unity between conservatives and radical reformists for the sake of the country at large. Within minutes of the end of his 2 1/2-hour address, conservative criticism of the Soviet leader already was spreading through the palace lobby, while outside the Kremlin walls anti-Communist protesters were chanting "Down with the party!"

Since the last party congress, a dramatic transformation has reshaped the political landscape of the Soviet Union and its former client states in Eastern Europe. The morale and public prestige of the Soviet Communist Party has plunged to sub-basement levels, while its long-unquestioned authority is being challenged by new political movements all around the country. Its membership is declining rapidly, and Gorbachev himself is widely criticized by Soviets of every political and ideological stripe.

The Soviet Union and the party that created it seethe with discontent -- fostered by failed visions and broken promises, by complicity with a guilty past, by political humiliation and material want, by a future it seems no faith can brighten. Since the turn of the century, Soviet party congresses have gathered at five-year intervals to review the issues and accomplishments of the past and correct the party's course toward the future. This congress, it seems, may have to start from scratch.

Historically, Soviet party congresses also have been used by the Kremlin to launch major new policies. The 17th congress in 1934, for example, was dominated by Joseph Stalin and set the stage for his reign of terror. The 20th congress, which took place three years after Stalin's death, was the setting for the so-called secret speech by new leader Nikita Khrushchev, in which he denounced Stalin for his crimes. Gorbachev used the 27th party congress to indict his predecessors for leading the country into economic and political stagnation and to outline his plans for reform.

The Gorbachev policy that has had perhaps the greatest effect on Soviet society since the 27th congress is that of glasnost, or open debate, and it, more than anything else, is responsible for changing the tone of the current party gathering. At the 1986 congress, before the spirit of openness became pervasive, the norm was for party officials to display a homogeneous public image. Conservatives such as then-KGB director Victor Chebrikov and Yegor Ligachev both sounded praise for Gorbachev's policies. Under glasnost, Gorbachev's ideological rivals voice their objections frankly, often with contempt.

Gorbachev's democratizing drive has also affected the style of this congress. The fledging free-election system in the Soviet Union has led to the growth of new political movements and parties in various regions. The change has undermined the Communist Party's monopoly on power and made it much more vulnerable to public criticism as the political fulcrum is shifting from internal party decisions toward debate in the newly empowered Soviet legislature.

The 4 1/2 years since the last congress have no doubt changed many of Gorbachev's perceptions, as well. Then, he clearly lacked a consensus in the party leadership to support radical departures from long-established policy, and he was hailed by the meeting for installing a new majority of his own men on the ruling Politburo. As it turned out, however, at least nine of the 13 members on that powerful body proved to be much more conservative than Gorbachev and worked to blunt his more far-reaching changes.

Political observers at the time also believed that Gorbachev's backers were a majority in the policy-making Central Committee elected at the end of the 27th congress, but that body also has consistently acted as a brake on radical reform. Gorbachev seemed unprepared in 1986 to endorse bold political measures, and his speech, heavily laden with Marxist-Leninist certitudes, attacked capitalism and "Western imperialism." In his speech today, Gorbachev stressed that a Western-style market economy is the only route that will save the Soviet economy, and he defended Soviet diplomacy that led to the overthrow of Communist governments throughout Eastern Europe.

The policies Gorbachev did endorse at the 1986 congress -- accelerated economic growth, higher goals for the Five Year Plan -- seemed easy enough for a broad-based body of Soviet Communist leaders to rally behind. He discussed the concept of his more fundamental perestroika restructuring, too, but did not elaborate on it until later. And he did not mention glasnost at all.