KIEV -- ''When I was six, I knew all that I know now that I am 60.''

The man who told me that is the man some admirers are calling the Lech Walesa of the Ukraine. His name is Mykailo Horyn, and with his younger brother Bohdan he supplies the great public passion and rudimentary political skill that has made Rukh -- the alliance of Ukrainian independence groups -- a growing force in this second-largest Soviet republic.

Bohdan Horyn is the leader of the new Republican Party, the most militant element in Rukh, in Lvov, the western Ukrainian city where independence sentiment is strongest. Mykhailo Horyn is the chairman of the Rukh secretariat, the coordinating committee for the whole republic. Both are members of the first freely elected Ukrainian parliament, now in session here, which last week formally asserted its sovereignty and independence from Soviet control.

In both its strengths and its weaknesses, Rukh is symptomatic of the independence movements that have emerged in the past six months to threaten fragmentation of the Soviet Union. Its idealism and its naivete spell both hope and danger.

Mykhailo Horyn and I were seated at a bare table in the shabby complex of offices, downhill from the parliament building, where Rukh has its headquarters. It is a warren of unlighted corridors and uneven floors. A visitor must dodge around a long-abandoned refrigerator in the hallway and ignore the stench from a broken toilet upstairs.

I had asked Horyn when Ukrainian independence had become his goal, and he answered, ''When I was born.'' His parents had been in the Ukrainian resistance movement, which fought first the Nazis and then the Russians. They were deported to Siberia for their actions.

The brothers are both short and stocky, with thick hair and bristling moustaches -- gray for Mykhailo and black for Bohdan, who is seven years younger. Their most striking features are the burning eyes of the true believer.

I had met Bohdan Horyn a night earlier, as the last light faded in a room of the Writers' Union. Long after the rest of his face had faded into shadows, his bright eyes shone in the gathering darkness.

He told how he and his brother had been jailed by Brezhnev, but had emerged in the late '70s as leaders of the Helsinki Watch human-rights group in the Ukraine. The Republican Party, founded only last April, has its organizational roots in Helsinki Watch.

The Horyn brothers are uncompromising. For them, the Soviet Union is ''the empire,'' and Mikhail Gorbachev is simply the man trying to halt its inevitable decline. ''In order to keep power, the imperialists talk of a new foundation, but we completely reject such talk,'' Bohdan Horyn said.

They are equally uncompromising in their demands. ''To me,' Mykhailo Horyn said, ''sovereignty means an independent Ukraine, with our own army, currency and banking system. And complete control of our own destiny.''

Rukh has its skeptics -- and its critics. The editor of Kiev's largest newspaper, a man who regularly finds fault with the Communist regime, says that an immediate move for independence in the Ukraine ''would produce civil war.'' Even Rukh partisans concede they have much less support in Kiev and the eastern Ukraine than in the western Ukraine where the Horyns were raised. Velodja Pastukhov, a political scientist now working in Moscow, notes that 40 percent of the republic's population is non-Ukrainian. He argues that large numbers of Russians and Jews in the Ukraine have grave misgivings about Rukh's brand of nationalism.

The Jewish question is a particularly sensitive one for Rukh leaders, given the area's history of anti-Jewish pogroms. Mykhailo Horyn stressed to me that Rukh had several Jews in its leadership, was establishing three Jewish cultural centers in Kiev, had issued three statements decrying antisemitism and had sent a prominent Jewish psychiatrist from Kiev as its first unofficial ''envoy'' to the West.

But a Ukrainian geography teacher I met while doing random on-the-street interviews in Moscow said that while he admired Rukh's ideals, ''I fear the people who have come under its banner.'' Since Rukh came to power in his home city, he said, antisemitic slogans have been scrawled on the walls of the elevator in his apartment building, ''and my children for the first time are afraid."

As worrisome to many, including the editor and the political scientist, is the blithe assumption the Horyns and other Rukh leaders make: that once independence is achieved, productivity will increase, investments will arrive from abroad and prosperity will quickly follow.

The Rukh leadership is heavy with heroes of past imprisonment, artists and intellectuals. But it is light on economists and engineers. Governmental experience is inevitably lacking among these non-Communists. ''They appreciate the cultural heritage of the past far better than the economic challenge of the future,'' political scientist Pastukhov said.

But Bohdan Horyn has a simple reply to all the doubters: ''Just let us try governing our land our way. We claim that right.''