TURMOIL IN THE EAST BLOC : Tehran Says Soviet Troops Block Border : Azerbaijan: Thousands of Soviet Muslims have reportedly crossed into Iran, returning with weapons.

Soviet troops deployed along the Iranian frontier with troubled Azerbaijan on Monday to block cross-border movement by Azerbaijanis on both sides, Tehran Radio reported.

Tens of thousands of Soviet Muslims reportedly have crossed into Iran in the last week. According to press reports from Moscow, many of them have returned to Soviet soil carrying weapons.

Iran’s official radio said that mechanized units of the Soviet army fanned out along the border west of Astara, a town just north of the frontier on the Caspian Sea coast. The broadcast, monitored in Nicosia, reported that no movement south across the border was being permitted but that Soviet Azerbaijanis who had crossed into Iran were being allowed to return under “strict controls.”

But in Moscow, the Soviet news agency Tass said that “the situation remains complicated on the state border. Azerbaijanis and Iranians continue to cross the border en masse in both directions.”

The extent of the attempt to seal the border was not clear. When violence erupted earlier this month between Soviet Azerbaijanis and Armenians, Azerbaijanis started forcing their way across the frontier into Muslim Iran several hundred miles west of Astara, along the Araks River separating Iranian Azerbaijanis from their Soviet kinsmen in the autonomous republic of Nakhichevan.

Soviet and Iranian border officials met Monday in Astara to discuss measures to control movement in the frontier zone, Tehran Radio said. No specific results of the talks were given.

20,000 Crossings

The Tehran broadcast said that more than 20,000 border crossings had been reported in the last four days. Crossing points, it said, were established at Astara and nearby Bilehsavar to permit the return of Soviet nationals. All other passage across the 400-mile-long border was reportedly forbidden.

Over the weekend, the Soviet government daily Izvestia charged that Iranian Azerbaijanis were crossing the Araks and sending guns over the border to help their kinsmen on the Soviet side. Tehran newspapers have denied the accusation but have widely reported the crossings of Soviet Azerbaijanis, who, according to these reports, carried out a demonstration on Iranian soil in support of the Ayatollah Ali Khamenei, Iran’s Shiite Muslim spiritual leader, and attended Muslim prayer services last Friday.

Hard-line Iranian newspapers decried the Soviet military assault in Baku, the Azerbaijani capital, to quell the unrest, terming it a massacre. According to an Iranian television report Sunday, President Hashemi Rafsanjani ordered Foreign Minister Ali Akbar Velayati to “take serious steps to solve problems and end bloodshed and violence” in the neighboring Soviet republic.