Underground Solidarity leaders have appealed to workers in the capital to organize their own May Day celebration, as they did last year when tens of thousands marched peacefully through the city's Old Town section in defiance of martial law.

A communique signed by three fugitive officials of the outlawed independent trade union linked the May 1 action to Pope John Paul II's planned visit in June. They also complained of police harassment against organizers of the unofficial event, which would compete with the government's traditional celebration of the international workers' holiday.

Meanwhile, more than 500 former martial-law internees and union activists have forwarded an open letter to the Polish leader, Gen. Wojciech Jaruzelski, and the Roman Catholic primate, Cardinal Jozef Glemp, accusing the government of ignoring "the aspirations of a major part of society." The letter lists seven demands, including an amnesty for all political prisoners, to be met before the pope arrives for his scheduled six-day return pilgrimage June 16.

The statements, which reached western correspondents here today, seemed to signal a stiffening of open resistance to authority and the rise of opposition activity linked to the papal visit.

Opponents of the government face the challenge of pressing their demands without inciting street protests that could give Communist officials a pretext to cancel the pope's trip.

Polish authorities, in turn, have made clear their determination to stand by the unpopular but officially sanctioned trade unions and citizens' action groups and to sustain a police crackdown against political underground operations. But the Jaruzelski government is at the same time under mounting pressure to make some goodwill concessions in connection with the pope's visit that would retrieve its lost credibility and encourage a lifting of western economic sanctions.

In a separate bulletin also received today, a group calling itself The Helsinki Committee in Poland announced its formation and vowed to hold the Polish government publicly accountable for violations of the 1975 international accord on European security and cooperation.

The committee said its membership would remain anonymous in view of "the existing situation" but said its reports would be "authorized by institutions or persons who enjoy authority and social confidence."

Its first report, covering human rights violations in Poland under martial law, was issued March 17 and passed to the Helsinki review conference in Madrid, the statement said. It added that the report's authenticity was guaranteed by Solidarity's underground Provisional Coordinating Committee.

May Day, which is traditionally celebrated throughout the Soviet Bloc, last year spurred the first major pro-Solidarity demonstration in the Polish capital after the imposition of martial law in December 1981. Interior Minister Czeslaw Kiszczak said last week that the government was bracing for new protest actions in early May, suggesting that such demonstrations were being promoted by western intelligence agencies intent on scuttling the pope's trip and stirring unrest in Poland.

Last year's May Day demonstration, which appeared to take authorities by surprise, was followed two days later by violent street clashes between pro-Solidarity marchers and police.

The underground statement was signed by Zbigniew Bujak, former chairman of the Warsaw regional Solidarity branch, and two other union activists still in hiding--Zbigniew Janas and Wiktor Kulerski.

The open letter from former internees to Jaruzelski and Glemp was signed by 62 workers representing factories throughout the Silesian mining region. The letter was discussed and approved Sunday at a meeting attended by more than 500 labor activists at the Jasna Gora monastery in Czestochowa, according to several participants in the meeting.

A copy of the letter was sent to the pope with a covering note containing a prayer for Poland's "wrongdoers and oppressors, exploiters and spreaders of lies" to "return to their senses in time" for John Paul's arrival in June.