TODAY the Soviet Communist Party opens a meeting of its top leadership that figures to be a crucial turning point in its history.The party's policymaking Central Committee gathers for two days to vote on a draft program, its first since the early 1960s. The program, according to a version published this week, repudiates Marxist-Leninist ideology and the party's clandestine, revolutionary traditions. Instead it offers an image and platform virtually indistinguishable from the parliamentary social democratic parties of Western Europe. In no uncertain terms, the draft program, reportedly prepared under President Mikhail Gorbachev's direction, rejects class struggle and the dictatorship of the proletariat. The goal of a communist society is replaced by a vision of a "new civilization" that "does not fit into the customary ideas of classic industrial society, with its sharp division into antagonistic classes." (See story, Page 3). The program will be the trigger for a sharp debate between the pro-reform and orthodox Communist wings of the ruling party, with much of the conservative fire aimed at Mr. Gorbachev himself. The battle at the Central Committee plenum has been widely advertised as the opening step toward a formal split of the massive Communist Party into two or maybe three parts. Gorbachev has won every past encounter with his party opponents, including one only last April when the conservatives made an abortive bid to oust him from the party leadership. He seems poised to win again, but in recent days the prospects for a far tougher struggle than earlier expected have risen. The most vocal opposition to Gorbachev comes from extremist elements who grouped themselves into the self-named Bolshevik Platform in mid-July. Led by neo-Stalinist Nina Andreeva, they oppose what she calls "the transfer of the Communist Party of the Soviet Union [CPSU] onto the rails of right-wing bourgeois democracy." A more serious expression of hard-line views was published on Tuesday in the daily Sovietskaya Rossiya by 12 conservatives including Deputy Defense Minister Valentin Varennikov and Deputy Interior Minister and Army hero Boris Gromov. With a direct appeal to the armed forces to join them, they call for creation of a "popular patriotic movement" for "the salvation of the Motherland." "How did it happen that we ... put in power those who do not love this country, who enslave themselves to foreign patrons and seek advice and blessing across the seas?" they ask, referring to Gorbachev's recent meeting in London with Western leaders. More troubling for Gorbachev are signs that he can no longer depend on the loyalty of the party center. Leningrad party leader Boris Gidaspov, while distancing himself from hard-liners, told reporters last week that Gorbachev's reforms amounted to "a replacement of Marxism by pure Darwinism, when the rich devour the poor." Moscow party boss Yuri Prokofiev, considered a moderate and a Gorbachev backer, called last week for Gorbachev to step down as party leader, and take a post as honorary chairman. Gorbachev can count only on the liberal wing of the party, which by most accounts includes about 100 out of the 412 members of the Central Committee. Many of the leaders of this group, such as industrialist Arkady Volsky, are members of the Movement for Democratic Reforms formed last month by former Foreign Minister Eduard Shevardnadze and eight other prominent liberals. The Communist right has assailed this move, which it views as a stalking horse for Gorbachev and the possible nucleus of a new social d emocratic party. Gorbachev will also depend on indirect backing from the leaders of the republics, such as Russia's Boris Yeltsin and Kazakhstan's Nursultan Nazarbeyev. Last April Gorbachev preempted a similar challenge from the right at a Central Committee meeting with the now famous April 23 "nine plus one" agreement with the heads of nine of the 15 republics on a the outlines of a new treaty of union. Gorbachev appears to be attempting the same thing now, with a meeting that began on Tuesday aimed at finalizing the treaty for ratification by republican parliaments. By press time yesterday with the meeting still continuing, the republics had reportedly settled all the issues except the nettlesome question of taxation. Russia and the Ukraine still oppose a federal tax. The Gorbachev-republic axis took a blow last weekend when Mr. Yeltsin banned all party organizations in government bodies and industrial enterprises, a move clearly aimed at the Communist Party and denounced by it as antidemocratic and a violation of existing laws. The decree will undoubtedly be a focus of the plenum, with conservatives citing it as evidence of the hostile nature of the democratic opposition. Gorbachev's spokesman took a somewhat careful tone, saying the decree disrupts the move toward accord, "causes anxiety, and introduces tension and confrontation." Yeltsin, trying to defuse its impact, told the Russian Information Agency that "my relations with President Gorbachev remain normal and there is no confrontation."