Lech Walesa, who headed the banned Solidarity labor union, disclosed today that he met over the weekend with leaders of Poland's underground opposition movement to coordinate positions.

The results of the clandestine talks were not given. A brief statement released by a Walesa spokesman said simply that the former union chief had conferred with the five-member provisional coordinating committee of Solidarity on Saturday, Sunday and Monday.

"They discussed in detail the country's present situation and coordinated their stands," the statement said.

It was the first such get-together between these two guiding authorities of the outlawed Solidarity movement and could mark a new phase in efforts by the former union leadership to outline a common front in seeking a workable agreement with Poland's Communist regime.

Since his release in November after 11 months of internment, Walesa has tried cautiously to build an opposition platform open to compromise with the government, while the underground Solidarity activists, who orchestrated antistate resistance during martial law last year, have taken a harder tactical line. In recent weeks, though, both Walesa and the committee have voiced support for each other's stands.

Their meeting now could signal a fresh initiative toward the government--an attempt, through Walesa, to take the underground above ground. Or, on the other hand, the secret conference could foreshadow a toughening of the opposition's stand toward authorities who, up to now, have rebuffed appeals for a national reconciliation based on an amnesty for political prisoners and a pluralistic trade union movement.

In any case, word of the surprise meeting can be expected to boost the morale of the government's critics. While the substance of what was discussed will likely emerge in time, just the fact of the conference stands out as a feat of daring: Walesa, presumably closely watched by security police, apparently managed to shake surveillance for a rendezvous with some of Poland's most wanted underground activists.

The underground committee members, all former senior Solidarity officials who evaded capture under martial law, include Zbigniew Bujak, Bogdan Lis, Wladyslaw Hardek, Jozef Pinior and Eugeniusz Szumiejko.

Asked for official comment, particularly concerning the prospect of Walesa's arrest, government spokesman Jerzy Urban said Walesa's action would be considered illegal only if the meeting involved scheming against the state or if Walesa had in some way provided assistance to the underground leaders.

Urban, speaking to foreign journalists at noon, said he had not heard about the meeting, which international wire agencies were reporting several hours earlier.

In the period before the planned June visit of Pope John Paul II, both the government and the opposition have stated their intention to avoid confrontation and to try to use the papal pilgrimage to achieve national reconciliation.

Urban sought today to downplay the strength of the opposition forces. Since passage last October of a new trade union law, he said, "Solidarity does not exist and Walesa is a private person."

He rejected suggestions that the political opposition in Poland is strengthening, saying that "underground documents are quite divergent, which shows that the authors aren't convinced of social support for their activities."