MOSCOW (AP) _ Helmeted riot police carrying truncheons and shields pushed protesters away from a square in central Moscow where demonstrators planned a rally today to support Russian Federation leader Boris N. Yeltsin.

''You should be ashamed 3/8'' one elderly woman shouted as a policeman in his teens pushed her over a curb near Manezh Square, the planned site of the pro- Yeltsin rally adjacent to the Kremlin.

The police who were not using their truncheons, pushed protesters gathering for the rally back up Tverskaya Street, away from the square. A light snow fell on the tens of thousands of protesters.

The police action came less than an hour before a pro-Yeltsin march through the city streets to the square was to start.

By nightfall, as the temperature dropped to freezing, police had compressed the protesters to a half-mile stretch of Tverskaya Street between Pushkin and Mayakovsky squares, north of Manezh Square.Pushkin Square is about a half-mile mile from Manezh Square.

The demonstrators then tried for a second time to march toward the Kremlin but at Pushkin Square they met a line of troops, who stood firm without making threatening moves. Water cannons were parked behind the troops.

Organizers, via loudspeakers, urged the marchers not to confront the soliders, and the demonstrators turned around, instead holding their pro- Yeltsin rally in Tverskaya Street.

''Yeltsin 3/8 Yeltsin 3/8'' people chanted. Many in Tverskaya Street stood atop telephone booths, trucks and newspaper kiosks, and hung out of windows.

The crowd waved tricolor pre-revolutionary Russian flags, shouted anti- Communist slogans and demanded Gorbachev resign.

One sign, carried by residents of Zelinograd, a small town outside Moscow, exhorted Yeltsin to ''Keep Going - Not One Step Backward.''

Other signs said ''Save Russia from the Communist Party,'' ''Say No to the Gorbachev Threat,'' ''The Communist Party is the Tyrant of Russia,'' and ''Communists, Go Home 3/8''

Hundreds of thousands of people had been expected for the rally in Manezh Square, but police succeeded in keeping it as well as Red Square, sealed off. Organizers urged participants to avoid conflicts with the police.

A line of police, five men deep, stretched across Tverskaya Street to keep demonstrators from reaching Manezh Square. They were backed up by a line of flatbed trucks as an additional barricade.

The crowd began gathering 2 1/2 hours before the scheduled start of march, but law enforcement agencies began moving early in the day. Thousands of troops, including police, Interior Ministry soldiers and others, poured into central Moscow early today. Water cannons were parked on side streets.

''If anybody starts anything, it will be the army,'' said Alexei Kuzmin, 33, one of about 100 Soviets who gathered at the corner of Manezh Square before the demonstration was scheduled to begin.

Complaining about the Gorbachev government's three-week ban on street protests, Kuzmin said: ''What did we vote for? Democracy? Human rights?'' He referred to the March 17 referendum on national unity.

''Look what they're doing to us now,'' he said, pointing to soldiers on the street.

Manezh Square was sealed off at its several entrances by flatbed trucks. Buses were parked in front of the Moscow Hotel at one side of the square where protest organizers had planned to speak.

Protesters carried pro-Yeltsin signs and some sold pro-Russian newspapers.

A 20-year-old engineering student, who would not give his name, said he was attending his first political demonstrations.

''I've never been involved in any group. But when I came out and saw troops, I decided I should join the demonstration tonight,'' he said.

Elsewhere in the city center, crowds number a few hundred massed on street corners.

They argued among themselves and with passers-by about Yeltsin and the Communist Party. Some jousted verbally with soldiers posted near Manezh Square.

Earlier, dozens of people gathered at the Tverskaya Street entrance to the square broke through light metal barricades shouting ''Yeltsin 3/8 Yeltsin 3/8'' and ''Gorbachev Resign 3/8'' Riot police later cleared them away.

Before the square was cleared, members of the Moscow City Council walked arm-in-arm away from the square, up Tverskaya Street to meet the other demonstration. They walked through two lines of police, who let them through, and they were followed by at least 1,000 people.