MOSCOW, NOV. 20 -- Soviet leader Mikhail Gorbachev, adopting a more cautious and moderate approach toward his bold program of political and economic reforms, today warned against extremism in Communist Party affairs with a speech that attacked both "conservatism and artificial avant-gardism."

In his first major statement since the firing of Moscow party leader Boris Yeltsin, reported by the official Soviet news agency Tass, Gorbachev appeared to be striving to resolve his first major political crisis in 2 1/2 years in power by building a middle-of-the-road consensus between the party's two radical wings, whose views he characterized as leading to political "dead-ends."

Gorbachev also called for an "antidogmatic" reappraisal of the party's role and urged party leaders to change their autocratic methods of rule in advance of major economic changes intended to streamline the Moscow bureaucracy and distribute more decision-making powers to the provinces.

While not mentioning Yeltsin by name, Gorbachev drew a historical parallel that indicated he was not softening his criticism of the deposed Moscow party chief, who had been one of the most fervent supporters of Gorbachev's reform program. Yeltsin was ousted Nov. 11 for committing "serious political mistakes," in particular a vehement attack at a Central Committee meeting in October against party leaders who want to slow the pace of reform.

Gorbachev said the lessons of the Communist Party's ideological struggles in the 1920s are "most instructive from the point of the present day." That period was marked by bitter debate and infighting in the party until Joseph Stalin emerged late in the decade as the undisputed leader following Lenin's death.

Party conflicts had arisen in part because of the personality flaws of certain leaders, Gorbachev said. "In such cases, personal amibtions, if they are inordinate and camouflaged with pseudo-revolutionary phrases and poses and with ostentatious concern for the higher goals and values, do much harm to the common cause," he said.

Tass quoted Gorbachev as saying that "conservatism and artificial avant-gardism . . . band together on the basis of committing an outrage upon reality as they seek to push it into dead ends -- those of outdated forms and dogmas on the one hand and those of abstract schemes which are dangerous for their demagogic aggressiveness or empty illusions on the other."

Yeltsin's ouster last week at a dramatic meeting of the Moscow party shocked the Soviet political establishment, and has led to petition drives by students and informal groups dissatisfed with the party's handling of the affair. Some Soviet and western analysts also have speculated that the harsh slap at Yeltsin will strengthen the hand of conservatives as important economic reforms take effect Jan. 1.

In his comments to the Central Committee, Gorbachev addressed those concerns by warning local party leaders to adapt to the "new requirements" of reform and democratization -- twin pillars of the Gorbachev program.

He also stressed the importance of keeping up the pace of change to stay ahead of a tendency to revert to old ways. A lag in the process can lead to "loss of momentum," he said. "And then some party organizations again resort to old methods to check the manifestations of some negative tendencies by issuing strings of orders.

"But now such methods won't do," he said. "This will only bring society in a fever, will unnerve people, bring nervousness into our political and ideological atmosphere, in public awareness."

He said old-fashioned dictatorial rule also runs counter to the reforms, which are supposed to broaden the rights of local managers, make them less dependent on Moscow and encourage greater efficiency across the country to bolster productivity.

"To bring pressure, to issue commands, to call everyone to district party committees are not a suitable method either," Gorbachev said, noting that the new economic system will unleash "the initiative of all sections of production and management."

"Hence, different approaches are needed. On a practical plane . . . the party at the present stage should somewhat reappraise its role of a political vanguard of society."

That role depends on the party's ability to keep up with new demands, Gorbachev said. Although Yeltsin was chastised for his outspoken comments, Gorbachev today encouraged frankness at party meetings. "There must be really hot discussions at meetings to report on the work done," he said. Attempts to suppress criticism will be made but they should be combatted, he said. "We greatly need adherence to {principle}."

Gorbachev referred in passing to the Moscow meeting on Yeltsin, echoing the view of those who said Yeltsin's shortcomings should have been aired earlier by other party leaders.

Broadening public participation in society is crucial for the success of reforms, Gorbachev said. "We have drawn the exceptionally important conclusion that we have incurred many losses because our reforms in the past were not backed up with sweeping political changes in terms of democratizing Soviet society."

He also stressed the urgency of getting ready for the reforms, which will shift 60 percent of the country's enterprises into a self-supporting system, allowing them to keep profits and to bear the responsibility for debts.

"I believe this question is vastly underrated in the party, in the economic management and work collectives," he said. "Not everyone has grasped the importance and seriousness of the matter."

Gorbachev strongly backed the role of the Soviet press in the reform process.

"In principle, the press has enhanced its militancy, but it should also get second wind, just as the entire party, the entire country. It should advance and not get stuck at yesterday's landmarks," he said.

Gorbachev's concluding comments indicated no change in the main themes of his program. "We have firmly embarked on the road of widening democracy and we shall continue to advance along the road of socialist democracy, consolidation of socialist values, freedom of thought and creativity," he said.