The leader of Poland's independent Solidarity trade union movement, Lech Walesa, voiced guarded optimism today about the outcome of planned negotiations with the communist authorities.

The Solidarity chairman was reporting to the union's national executive in Gdansk on the results of his summit yesterday with the Communist Party leader, Gen. Wojciech Jaruzelski, and the Roman Catholic primate of Poland, Archbishop Jozef Glemp. The three men discussed the possibility of forming a new consultative body to help overcome Poland's economic and political problems.

A similar expression of optimism about Poland's future came from Archbishop Glemp on his arrival in Rome, where he is expected to have talks with the Polish-born pontiff, John Paul II. Glemp said that as a result of yesterday's meeting he was more hopeful of finding a peaceful solution to the crisis.

State-run television tonight screened interviews with ordinary Poles praising the fact that the leaders of the three main social forces had for the first time held joint discussions on the country's future.

In a statement, Solidarity spokesman Mark Brunne said the fact that the talks had taken place was a reason to "regain lost hopes for the long-awaited reconstruction of social life in Poland." He said Jaruzelski had agreed that new talks should begin when the union was ready.

The statement quoted Walesa as saying that he was "a cautious optimist" about the results of new negotiations, which are expected to begin in a few days. The talks should carry the slogan, "Poles not only can, but must reach agreement in the face economic and social threats to the country," he added.

Solidarity has called for the talks to center on short-term measures designed to ensure that the country survives the coming winter, plans for economic reform and the introduction of more democracy to public life. A resolution passed by the union's executive National Committee yesterday set a deadline of three months for the negotiations.

Both sides have expressed a readiness to make concessions during the talks and not to stick rigidly to their opening positions. In view of the intractable nature of the issues involved, however, the negotiations are likely to be both difficult and prolonged.