About 20,000 striking steelworkers stretched their pay raise demand to 70 percent Wednesday after negotiations broke down overnight and Solidarity founder Lech Walesa called on Poles to press for "real structural changes" in their society.

The 2-day-old strike at the Lenin foundry in southern Nowa Huta is the latest and largest in a growing number of worker protests in the last week. On Monday, about 2,000 transport workers in Bydgoszcz and Inowroclaw won a 63 percent pay raise after they walked off their jobs demanding higher wages.Strike negotiators in Nowa Huta resumed talks with Communist Party officials, a source at the Lenin foundry said, but added "the chances to resolve the conflict are slim."

A Solidarity plant committee at the steel mill of Stalowa Wola in southern Poland also announced it would begin a strike Friday unless 25,000 workers receive a monthly pay raise of $52.

"The growing feeling of injustice and hopelessness are causing strike actions such as in Nowa Huta," Walesa said in a statement distributed among Western news agencies.

"Our union calls on all social forces to join their efforts to undertake common actions in solidarity to exercise the pressure on the authorities of People's Poland," he said, without specifying how these actions should be organized.

He said his outlawed union banned in 1982 supports strike actions that are "protecting the living standards of the people" and urged the regions of Gdansk, Szczecin on the Baltic coast and southwestern city of Wroclaw to start preparations for strikes.

Poles should exert pressure on authorities to "enter the road of real structural changes based on pluralism and social agreements," he said.

Walesa apparently was referring to a revival of the banned Solidarity union and the government's respect of the agreement signed between authorities and Solidarity in 1980 that legalized the operation of the first free union in the East bloc.

The growing dispute in Nowa Huta, near the southern city of Krakow, began Tuesday when some 10,000 people at the Lenin foundry walked off their jobs, demanding salary increases for themselves and 12 million of their countrymen.

Another 10,000 foundry workers who showed up at the plant at 6 a.m. today for their shifts joined the strike when they learned that talks between a strike committee and Communist Party officials stalled overnight. A total of 30,000 people work at the huge plant.