The Soviet Union, in the most menacing terms it has used so far, accused the Solidarity trade union federation today of launching an open struggle against Poland's communist government by preparing for a nationwide strike Tuesday.

The official Tass news agency, in a dispatch from Warsaw, claimed "anti-socialists, subversives, and extremists" had blocked a key provincial highway, assaulted post offices and a television transmitter, and seized food stores in a series of pre-strike provocations -- accounts that were promptly denied by Poland's state-run television.

Hungarian television, meanwhile, called for "vigilance" against what it described as recent events in Poland leading to "deliberate disintegration of a whole nation and a whole society."

The Soviet dispatch portrayed mounting anarchy in its strategically located neighbor and signled out KOR, the Committee for Social Self-Denfense, as ringleader of the alleged attempt to challenge the government.

Tass also accused President Reagan of attempted "gross interference" in Poland's internal affairs and of "instigation of forces opposed to the government." It said Reagan, in an interview with The Washington Post published today, "virtually demanded that the Polish government not take any resolute steps in connection with the dangerous situation in the country. By what right are such demands made of a sovereign state?"

It accused Reagan of "hypocrisy," and called on him to "cease interference in whatever form in Poland's internal affairs."

Soviet media broadcast the official view of conditions in Poland as the deeply divided Polish Communist Party Central Committee met in Warsaw. The Soviets seem dismayed at the ease with which Solidarity called workers off the job last Friday in a four-hour warning strike.

Moscow, thought certain by observers have to be pressuring the Polish party leadership as never before to adopt a tough new line against the independent union movement, described with outrage pre-strike instructions, which Tass said include plans by Solidarity for control of all state communications faculities, secret transport mobilization orders, purge lists and the gathering of home addresses of Polish militia and security forces.

While President Leonid Brezhnev and his Politburo have publicly kept silent about the newest episode in Poland's continuing economic and political crisis, escalating attacks by the official news media in recent days show the Kremlin is deeply agitated by the possibility of a crippling work stoppage.

A national strike could jeopardize Moscow's strategic supply and communications lines across Poland to its forces in East Germany, and deepen the economic turmoil in Poland. In addition, a major strike could have serious political repercussions elsewhere in the Eastern Bloc.

Tass said Solidarity's strike instructions, which the agency said had been printed in a Baltic Coast newspaper, "attest to the fact that this organization resorts to open methods of struggle against legitimate state authority -- against the government and the Polish [Communist] Party. The provocative instructions and brazen actions by the opponents of the socialist system show that KOR leaders, who are actually running Solidarity, are taking measures disregarding the republic's legitimate authorities."

"The situation in Poland is extremely tense," Tass said.