Former Moscow Party boss Boris Yeltsin, fired last year for pushing too hard for perestroika, asked for "political rehabilitation" Friday in a dramatic appearance at the 19th Communist Party Conference.

But Yeltsin also criticized the format of the conference, which was in its fourth day Friday. Yeltsin was among the last speakers in Friday's session and spoke shortly after a delegate denounced the Soviet invasion of Afghanistan.Yeltsin's request, reported by the official news agency Tass, came a day after a dramatic move orchestrated by Soviet leader Mikhail Gorbachev calling for the ouster of President Andrei Gromyko and three other aging Kremlin leaders. Gromyko chaired Friday's session because it was his turn under a system that has rotated the chairmanship daily.

Yeltsin was dismissed in November after criticizing the slow pace of the perestroika reform program. "As you know my speech was denounced as politically erroneous," Yeltsin said. "I believe my only mistake was I chose the wrong time, before the celebration of the October Revolution."

Yeltsin is known as an outspoken supporter of Gorbachev's policy of perestroika. He reportedly had told Gorbachev at an October plenum of the Communist Party that at its present pace "perestrlika was not giving the people anything."

Yeltsin's full remarks at that October meeting have never been published, though various versions of the speech have been reported - all of which Yeltsin has said do not reflect what he really said at the time.

Yeltsin, who was replaced as Moscow Party boss by Lev Zaikov, now occupies a minor ministerial post in Moscow. Yeltsin was elected a conference delegate from Karelia in the north of Russia, in a still-unexplained selection seen as an act of protest in support of his views.

Earlier, Grigory Baklanov, editor of the literary journal Znamaya, praised Gorbachev's decision to withdraw the troops from Afghanistan this year, more than eight years after they entered to bolster a faltering pro-Soviet regime.

"But the other decision _ the one to move the troops into Afghanistan _ has been taken in defiance of the machinery of democracy," Tass reported Baklanov as telling the nearly 5,000 conference delegates.

Tass, providing running summaries of the speeches at the conference, said the respected writer called "for creating guarantees to prevent anything of the kind from recurring ever again."

In Gorbachev's speech opening the 19th Party Conference Tuesday, he attacked the previous Soviet leadership and spoke of foreign policy mistakes, which observers took to include the ill-fated December 1979 invasion of Afghanistan.

The conference, which is to produce resolutions on Gorbachev's reform program of perestroika, democratization, the economy and the bureaucracy, got off to a slow start Tuesday. But since then, speeches have touched the most pressing problems facing the Soviet Union.

Fyordor Morgun, chairman of the Soviet Committee for Environmental Protection, warned about the "grave ecological situation" created by the traditional drive to create massive industrial complexes.

Morgun said that soil fertility is dropping, water quality has deteriorated almost everywhere and the air pollution "of all the industrial centers" does not meet health standards, Tass reported.

Thursday, an obscure delegate from the Komi region took the rostrum and _ spurred by Gorbachev to name names _ promptly called for the removal of four officials including Gromyko, 78, and fellow Politburo member Mikhail Solomentsev, 74, both holdovers from now disgraced previous regimes.

In his unprecedented attack on the party elite, Vladimir Melnikov, head of a Siberian regional party organization, also named "Afanasev" and Arbatov" as leaders who should step down to allow for Gorbachev's proposed reforms.

Georgi Arbatov is a foreign policy expert with the government's USA and Canada Institute and Viktor Afanasev is the editor of the party newspaper Pravda.

Gromyko and Solomentsev were seated near Gorbachev because of their membership in the 13-man ruling Politburo but neither showed emotion. All four men are viewed as opponents of sweeping political reforms advocated by Gorbachev.

Those proposals include a complete overhaul of the electoral system to include multicandidate elections, limiting elected officials to 10 years in office and giving more power to popularly elected Soviets and easing party meddling in the day-to-day running of local affairs.