Strikes spread for the first time today to the important mining and industrial region of Silesia as a strike leader here announced that negotiators are close to a major breakthrough on the key issue of independent trade unions.

Workers at the Lenin Shipyard here applauded at reports, later confirmed by the government, that 20,000 miners and factory employes in Silesia had joined the walkout, which now involves more than half a million workers nationwide.

Silesia is the political power base of Poland's Communist Party leader, Edward Gierek. The strikes there are likely to be another blow to his efforts to hold onto his already shaky position.

Lech Walesa, leader of the Gdansk shipyard workers, said here that a mixed committee of government and strikers' representatives had reached "90 percent agreement" on the demand for new, independent unions.

But Walesa warned that the fact that a working-level subcommittee had reached a large measure of agreement did not mean that it might not be overruled by higher authorities.

A full meeting of the strike committee, which represents 500 factories along the Baltic Coast, and a government commission was scheduled for Saturday morning to examine the subcommitte's findings.

But there were complaints among strike leaders that the government was dragging its feet and speculation that there were confusion and discord among the country's leadership about how to handle the issue of independent unions.

"The government is doing whatever it can to hold up the talks," said Bogdan Lis, a strikers' representative on the negotiating committee. "It therefore bears the entire responsibility for the strike's continuation."

Walesa's optimistic statement followed repeated warnings by senior government and party officials of a possible catastrophe for Poland if the strikes continue.

Walesa called on delegates to the strike committee to return to their own plants and inform workers of the apparent progress. He said: "We are making progress. The situation is all right. We begin to understand each other."

If agreement can be reached on independent trade unions, considered the most sensitive of the 21 original demands by the strikers, it is thought that the other issues involving political and economic reforms can be quickly settled.

Strike leaders have emphasized the need for free trade unions, saying that in their view some permanent mechanism is needed to ensure that the Communist Party authorities do not later retreat on promises for reform.

Such a move, however, could diminish the party's leading role in the country, a step against which the Soviet Union and many of Poland's leaders have cautioned. [In a message apparently intended for the Soviets, U.S. Secretary of State Edmund Muskie said today that "the United States government will refrain from any words or actions which might complicate the resolution of Poland's current difficulties in a manner consistent with the aspirations of its people." ]Muskie's statement added that the United States "views with sympathy the efforts of the Polish people and government to reach solutions to their current difficulties consistent with the aspirations of the people and the traditions of their nation, and free from outside interference."

Earlier in the day, the news that 20,000 workers in Silesia were supporting the strike had been greeted with loud applause in the Lenin Shipyard.

The reports of strikes there were confirmed by the government information agency, which spoke of labor unrest around the towns of Rybnik and Bialsko Biala near the Czechoslovak border. It said some coal mines, the main source of Polish exports, were among the plants affected.

From the north, the strikes have now spread through much of western and southern Poland. Interfactory strike committees have been set up in several towns, including Lodz, Wroclaw and Gubin on the East German border. Public transport has also been brought to a standstill.

In Poznan, in western Poland, public transportation also came to a halt and workers in some plants downed tools in solidarity with the strikes on the Baltic Coast. Poznan was the scene of antigovernment riots in 1956.

According to a strikers' spokesman in Gdansk, an integrated strike committee has also been set up to represent the demands of the Silesian workers. A delegation from the committee was reported to be on its way here to observe negotiations with the government commission.

Despite growing anxiety among senior Communist officials, the mood among strikers in Gdansk remained calm and unhurried throughout the day. Random groups questioned by foreign journalists said they would refuse to go back to work until granted free trade unions.

The latest slogan to be pasted onto the walls of the plant in "21 x Tak," meaning "yes" to all 21 of the strikers' demands.

The strike committee here earlier forward a proposal for the establishment of free trade unions to the government commission headed by Deputy Premier Mieczyslaw Jagielski. Among the most important points was a request for an amendment to the Polish constitution defining the rights of the new unions.

Under the strikers' proposal, the new trade unions would not be entitled to play the role of a political party, nor would they challenge the basic foundations of Poland's one-party-system. The sole purpose of the new unions would be to represent workers' interests.

For its part, the government was asked to represent the structure and official unions, which would remain in existence.

So far the government has yet to concede publicly the principle of fully independent unions, and an editorial in the Communist Party newspaper Trybuna Ludu today stressed that "The unity of the working class movement cannot be split."

It also reaffirmed Poland's unswerving loyalty to the socialist camp and its close links with the Soviet Union, denouncing West German press commentary suggesting that the workers' movement was leading to a "reorientation of Poland toward the West."

In the negotiations underway between the government and strike leaders, an official spokesman earlier said Jagielski would not return for more talks at the Lenin yard until agreement had been reached in the subcommittee of experts.

A plenary session of negotiations planned for this morning was canceled after a telephone call from the regional administration.

Kazimierz Barcikowski, another deputy premier, said tonight he had failed to negotiate an end to strikes in the western port of Szczecin, despite eight meetings with strike leaders there.

Barcikowski, performing the same negotiating task as Jagielski is doing in Gdansk, said on national television that the issue of free trade unions remained the controversial problem. "From the very outset, the biggest difference of viewpoint has been over the unions," he said.

But, with the strikers unwilling to budge from their demand of unions, the outcome of the crisis appeared to hang on a political battle being fought behind the scenes in Warsaw. The government was faced with the dilemma of either having to make fresh concessions on a point of principle or contemplate the use of force to break the strikes.

Today, the last Friday in the month, was payday for Polish workers, but even the sight of smaller pay packets does not appear to have lessened the strikers' resolve.

The shipyard workers, who have been on strike for just over two