MOSCOW -- Boris Yeltsin, leader of the Russian Republic, met for two hours last week with supporters in the democratic movement to throw down the gauntlet to Mikhail Gorbachev and the Communist/secret police/military juggernaut now allied with him.

Just as screws were tightening in the Soviet Union with Gorbachev's acquiescence if not direction, Yeltsin-led democrats challenged him. They defied Gorbachev's edict that his March 17 referendum be limited to voting on keeping the Soviet Union in its present state, and instead added radical issues to the ballot in Russia, the biggest and most populous of the Soviet republics. The democrats also decided to oppose Gorbachev's price increases because they are unaccompanied by real economic reform. Over Soviet television last night, Yeltsin called on Gorbachev to resign.

That bold course coincides with fear that escalating repression will be climaxed by efforts to oust, arrest or even kill Yeltsin. His chauffeur-driven car has been in four crashes the past year, hospitalizing Yeltsin once with serious injuries. "Every time, I have to think: Was that really an accident?" he told us.

How far the Soviet clock has been turned back will be revealed by what the state does with this troublesome challenger. Barring another "accident," it will be difficult to dispose of Yeltsin. He is the Soviet Union's most popular political figure (polls show 60 percent approval to Gorbachev's 15 percent) and embodies public revulsion at 73 years of Communist misrule.

Yeltsin long has been the populist hero of the Russian masses, but since our last visit here six months ago he also has become Andrei Sakharov's unchallenged successor as leader of the intellectuals who dominate the reform movement. They have erased doubts they harbored then as to whether this former apparatchik was truly committed to reform and democracy.

He pounded home to us support for those causes during nearly two hours of questioning. He pulled no punches about the Soviet crackdown or help for it, however unintentional, from President Bush and Secretary of State James A. Baker III, through loyalty to Gorbachev.

Yeltsin linked Gorbachev to a Communist Party clinging to its formally abandoned commanding role and the KGB ("a monster . . . a mammoth state within a state"). But the army, he continued, is split and "can fail to support the president." As for the people, Yeltsin said Gorbachev is concerned about showing himself publicly -- and correctly so: "I wouldn't advise him to travel within the country at present. The situation is very tense, very tense."

The tension, according to Yeltsin, will bring "civil war" only if troops enforce economic decrees. "On the whole," he told us, "I don't think the military will fight against the people. The KGB? Maybe some of its divisions -- specially trained ones. Maybe. But that will not be decisive."

Yeltsin told us his pro-reform coalition with Gorbachev last August ended after "I noticed something: once we agreed about something, he failed to live up to the agreement." Gorbachev had succumbed to "the {Communist-KGB-army} apparat, which was to be dismantled as part of the {reform} process." To Yeltsin, this regression is facilitated by Washington. "It's high time Mr. Bush and Mr. Baker clearly saw processes that are underway in the Soviet Union . . . " he said. "The republics have proclaimed their sovereignty, and they're going after it."

While saying "I have received certain signals from Baker inviting contacts," Yeltsin added, "I think the time is coming to establish a contact with the U.S. president." He would like an invitation to Washington from Bush, though such a rebuff to Gorbachev is most unlikely.

Yeltsin, now president of Russia by vote of the republic's Supreme Soviet, told us he plans to seek the office by direct election. The elected leader of 150 million Russians would be hard for the White House to ignore. But when we asked Yeltsin when the election would be held, his answer reflected the foreboding prevalent here: "April or May, unless there's an explosion of the entire situation before that."