Protesters, provocateurs, and police mix it up in Moscow. SOVIET CRACKDOWN

``I decided to move here because after three years of perestroika [restructuring], there have been no real changes,'' said a young man, explaining to a crowd of bystanders why he had joined Saturday's demonstration in central Moscow. He was, in fact, talking after the main demonstration had been broken up. Twenty minutes earlier, groups of police and plainclothesmen had dived into a crowd several hundred strong and pulled out about half a dozen demonstrators.

This was the first time in four weeks of such demonstrations that the police had cracked down. And it was, one prominent activist said, ``a blatant provocation by Yegor Kuzmich [Ligachev] and his bandits.'' Mr. Ligachev is the second-ranking Soviet leader and is widely considered to take a markedly more conservative approach to reform than party chief Mikhail Gorbachev.

The dispersal of the demonstration is one of several recent moves by the authorities that have put a chill on the run-up to the Communist Party conference that will soon bring 5,000 delegates to Moscow to discuss reform. These include instructions to the media to moderate their sharp criticism of the way delegates to the conference had been elected. The demonstration had, however, returned to this theme. Its leaders were agitating for the formation of a Popular Front, which they describe as a mass organization to support Mr. Gorbachev's push for radical reform.

The crackdown was carefully planned. A police general was on hand to direct operations, though at one point he took refuge in a subway station to avoid persistent questioning by an irate crowd. The numbers of police and plainclothesmen were considerably greater than on the previous Saturday. Some police were well drilled.

``Whatever you do,'' Maj. Lev Birman told his men, ``smile.'' Demonstrators complained that KGB (secret police) provocateurs were active among the crowd.

By an interesting coincidence, one suspected provocateur was known to this correspondent. Burly and bearded, dressed in denim jacket and jeans, with tattoos on his knuckles, he was standing on a wall, yelling his support for the Popular Front. When a police major came within range, he shouted anti-police slogans literally into the officer's face. A few minutes later he was dragged away and thrown dramatically into a police bus.

The last time I had met this man, he was soliciting for support for an organization at the other end of the political spectrum from the Popular Front - the anti-Semite Pamyat (memory). At that time he said that Pamyat was organizing armed self defense units, and asked for help with printing equipment.

Four hours after Saturday's arrests, the same man and a colleague were there again, haranguing a small crowd.

Dispersing the demonstration was only a partial success for the forces of order. People seemed less cowed than they had before in the face of the police. And their response was more sophisticated.

As the police cordoned off the demonstration area, two people engaged a young policeman in conversation. ``How do you feel about doing this,'' asked a woman who looked roughly the age of the policeman's mother.

``Look, I'm wearing a uniform, I'm doing my duty,'' he answered a little defensively.

``What would you do if they told you to fire on a demonstration?'' a young man asked. ``It won't come to that,'' the policeman answered anxiously.

``But why are you here? Why can't people demonstrate?'' he was asked.

``I'm just a little person. Don't ask me, ask the comrade general. I have to do this. I swore an oath.''

``Who did you swear an oath to, the people or your commanders?''

``I'm a small cog,'' he protested.

``A small cog in a big repressive machine?'' the man asked.

``Look, as a human being I can sympathize with you,'' the policeman finally said. ``But I'm wearing this uniform. What can I do?''

Small knots of people continued to stand around, debating politics, after the main body of police retired to their buses. The response to Popular Front activists from passers-by seemed less hostile than in previous weeks. One activist was asked why the demonstration had denounced the selection of the mayor of Moscow, Valery Saikin, as a delegate to the party conference.

``Saikin's a retrogade,'' a demonstrator explained. ``He doesn't even understand what democracy means. And the people who elected him [to be a delegate] knew that, but they just raised their hands and kept quiet. That's why reforms are in trouble.''

Nobody challenged his description of Mr. Saikin, a member of the Communist Party Central Committee, or his assertion that reforms were in trouble.

Another passer-by, a middle-aged woman who had been questioning the demonstrator closely, peeled off from the group. ``I wish you luck,'' she said, adding as an afterthought, ``I wish us luck.''