MOSCOW (AP) _ Striking workers at the country's largest coal mine returned to work today after the Russian Federation agreed to take over control of the pits from the national government, their union said.

The return to work was the first major crack in a nearly 7-week-old strike that spread to all major coal fields and curbed production in other industries.

The walkout has battered the already reeling Soviet economy and posed a strong challenge to Soviet President Mikhail S. Gorbachev's authority.

The official Tass news agency quoted mine director Alexander Yevtushenko as saying coal shipments from the Raspadskaya mine in western Siberia would resume Thursday.

Yevtushenko was quoted as saying the mine - the first to sign an agreement with the Russian Federation - would be converted into a joint-stock company, a limited form of private ownership in which companies and individuals could purchase shares.

It was not immediately known how many miners went back to work today.

The strike began March 1, and triggered sympathy strikes in some industries and strike threats by many others. About 300,000 of the country's 1.2 million miners joined in the walkout at more than 100 of the country's 600 mines.

The return to work by some miners came one day after the Supreme Soviet legislature gave preliminary approval to a law banning political strikes, which some lawmakers called that a step backward for the country's fragile democracy. The development also came as Gorbachev was on an official visit to Japan.

The strike were the first nationwide test of strength of the Independent Union of Miners, founded last fall after the government failed to fulfill many of the promises it made to end a series of strikes in the summer of 1989.

The coal miners began with demands for higher wages and better working conditions, but added political demands, including Gorbachev's resignation and the dissolution of the Supreme Soviet.

Earlier this month, the government offered to double miners' wages if production rises, but the miners refused to return to work, saying the wage increases would quickly be swallowed up by inflation.

The miners want their wages - and all workers' wages - indexed to inflation.

Gorbachev issued a decree on Friday giving officials of the republics and local governments one week to resume deliveries of raw materials and other goods from their regions. Several plants have been closed because of the shortage of coal.

A miner now makes 375 rubles a month, or about $665. That is 40 percent more than the average Soviet worker.

The striking miners are also demanding to retire after 25 years work underground. There currently is no limit on most miners' years of service.

Mining is one of the most hazardous professions in the Soviet Union due to inadequate safety measures. The average life expectancy for miners if about 52, far less than Soviet workers as a whole.

Vyacheslav Sharipov of Siberia's Kuznetsk coal basin strike committee, which remains on strike, said the back-to-work decision ''has brought some confusion.''

''Other guys from other mines have not been happy to learn about it,'' he said in a telephone interview. ''At the very start, we agreed that the decision to end the strike should be reached together.''

Another Kuznetsk spokesman, Sergei Verenkov, said representatives of other Kuznetsk mines were scheduled to meet Russian Federation Prime Minister Ivan Silayev in Moscow on Thursday.

Silayev said last month the largest and most resource-rich Soviet republic was willing to assume jurisdiction of hundreds of mines in Siberia and the Ural Mountains. The takeover was one of the miners' demands.

The mine formerly was run by the national Coal Ministry, meaning all decisions about production and sales were made in Moscow.

''The country's largest coal mine is now flying the (Russian) flag instead of the Soviet one,'' said the independent Postfactum news agency.

The Raspadskaya mine is capable of producing 20,000 tons a coal a day, Tass said.

The coal strike has forced scores of Soviet steel, iron and chemical plants to close or drastically cut production. Soviet news reports have said the ''chain reaction'' from the strike left the country short of steel, affecting every major branch of industry.

Soviet television says the strike has meant lost production of 5 million metric tons of coal worth 500 million rubles, or $850 million.

As the miners strike dragged on, thousands of workers in other industries have walked off their jobs in recent weeks to make similar demands for higher wages and Gorbachev's resignation.

In Minsk, the Byelorussian capital, tens of thousands of workers went on strike last week but returned to their jobs when the republic's leaders agreed to begin talks.