Poland's military authorities yesterday broadcast tape-recorded conversations between underground leaders of the outlawed Solidarity trade union that took place during supposedly secret strategy sessions.

The radio broadcast, which had been well-advertised in advance, came as several martial-law regulations were lifted and others were replaced with new emergency regulations. These actions were taken as part of the official "suspension" of martial law throughout Poland, which came at midnight last night as expected.

The broadcasting of the tapes of the underground meetings is likely to come as a heavy blow to the fragmented remains of Solidarity's once impressive organization. It could foreshadow the arrests of more underground activists who went into hiding after the military crackdown on Dec. 13, 1981.

The tapes, broadcast last evening on a prime-time radio show that lasted 90 minutes, included a meeting last month of Solidarity's provisional coordinating commission that was attended by at least six underground leaders. Other tapes featured fragments of recent conversations including Zbigniew Bujak and Bogdan Lis, the underground leaders in Warsaw and Gdansk.

An announcer said the tapes had been recorded and made available by officials of the Interior Ministry. This implies either that the apartments in which the underground leaders were meeting had been bugged or that there was a secret police agent in their midst.

Another possibility is that the Solidarity activists recorded their sessions and the tapes were discovered by the police during recent raids on underground hideouts and printing houses.

Wherever the tapes came from, the fact that the government is now able to broadcast secret meetings of the underground is likely to have a serious effect on the morale of Solidarity activists. The message the program left with Poles who listened was that the secret police now exercise virtually unlimited control.

The content of the tapes was not as startling as the fact that they were broadcast. The discussion followed the lines to recent debates in underground Solidarity publications, over how to organize continuing resistance to the martial-law regime following the failure of a planned eight-hour nationwide protest strike on Nov. 10.

The recordings were interspersed with music from James Bond films in an apparent effort to mock the underground's attempts at clandestine activity. In a discussion afterward, the underground activists were depicted as "cynical gamblers" interested only in politics and not in the welfare of ordinary workers.

The first taped conversation was between Bujak, who has become a hero to Solidarity activists because of his underground activities, and an unidentified colleague. It took place before the Nov. 10 strike and centered on what Solidarity would do if the protest failed.

Bujak was heard saying that the struggle would have to continue by other means.

The two men discussed the possibilities of forming underground political parties amd stepping up education of the workers.

Bujak indicated that he was strongly opposed to the use of terrorism by Solidarity, but believed that the underground's failure to achieve its political goals could lead to uncontrolled terrorism.

The second tape featured a meeting of Solidarity's six-man provisional coordinationg commission apparently at the end of November. The meeting discussed the release from internment of Solidarity leader Lech Walesa and the poor response to the call for strikes and demonstrations on the second anniversary of Solidarity's legal registration.

The participants were heard to agree that most Poles were tired of protest actions such as strikes and demonstrations and there was little chance at present of again organizing an independent union movement. They also stressed the need for ending all public speculation of a rift between the provisional commission and Walesa.

The government's version of how the tape recordings came to be made, suggesting that the underground leadership is infiltrated by the police, raises the question of why Bujak and other Solidarity activists are allowed to remain at liberty. A possible answer could be that the authorities preferred to allow the underground to be led by known figures whom they could try to manipulate, rather than by lower-level and possibly more radical activists.

The interior minister, Gen. Czeslaw Kiszczak, is a former head of military intelligence. Arrests made by police under his jurisdiction often appear to have been timed to coincide with propaganda points that the government wishes to make.

The decision to suspend martial law is unlikely to have much immediate effect on the lives of ordinary Poles.

Telephone conversations will no longer be openly monitored and the recorded "This conversation is being controlled" that has accompanied every call is to be dropped. The government said other telecommunications restrictions would be relaxed and direct-dial calls between Poland and other European countries restored.

Stringent provisions have been written into the penal code, however, to prevent any surge of social unrest and many factories will remain under military-style discipline