Pope John Paul II held lengthy talks here today with the first special emissary to arrive from the Roman Catholic Church in embattled Poland, then publicly signaled the esteem in which he continues to hold detained labor leader Lech Walesa and the "free Polish union, Solidarity."

Despite continued secrecy about the pope's diplomatic efforts, he made his sentiments clear in his annual "State of the Church" speech delivered to the College of Cardinals, Curia officials and Vatican employes at midday today. "I still remember with emotion the audience with Lech Walesa," the Polish-born pope said of a meeting last January, "and the message I gave him and . . /. Solidarity."

Sources inside the Vatican have indicated that the pope considers Walesa a key to any peaceful negotiated settlement of the Polish crisis.

Vatican analysts believe that the only way out of the Polish impasse, which they fear could lead still to a Soviet intervention or even a war, has to be a compromise that would lift the ban on Solidarity's activities imposed by the Polish leader, Gen. Wojciech Jaruzelski, when he declared martial law, in return for an agreement by the workers to limit their demands and increasingly costly strikes.

These sources said that Walesa, a moderate within Solidarity who was increasingly challenged by militants, should be supported and built up because only he has the national prestige in Poland that could sell a compromise to the workers when and if it could be mediated by the pope or his emissaries.

Archbishop Jozef Glemp, the Polish primate, has so far refused to hold any direct talks with Jaruzelski as long as Walesa and other Solidarity leaders remain under arrest.

The government, in turn, has refused all demands to free the detained leaders. In a message last week the pope called on the Polish authorities not to renounce the "renewal" of Polish society that Solidarity's pressures for freedom of expression, for the right to organize unions and to strike and for other reforms, had begun.

Vatican spokesman Romeo Pancirolli said that the pope had concelebrated mass in his private Vatican chapel this morning with Bishop Bronislaw Dabrowski, the secretary of the Polish episcopal conference who arrived from Warsaw last night, then met for more than an hour with the Polish church envoy to discuss the chances of papal mediation in Poland.

Sources earlier revealed that after his arrival, Dabrowski, the auxiliary bishop of Warsaw, was ushered immediately into the pope's private Vatican apartment to give the pontiff his first direct report on the crisis that has resulted from the military crackdown against Solidarity and other reformist forces, which was launched Dec. 13.

The exact details of the pope's discussions with Dabrowski have been kept secret. But his arrival, and the fact that after several days' delay last week the Polish authorities finally let him leave for Rome to report to the pope, were interpreted by Vatican officials as a "positive development."

Sunday the pope's own special envoy to Poland, Bishop Luigi Poggi, reached Warsaw by train to open discussions with church, state and, it was hoped, Solidarity officials.

Direct telephonic or telecommunication links between the Vatican and Glemp's archdiocesan offices in Warsaw have yet to be restored, but the traveling emissaries have at least managed to open up a line of communication that, Vatican sources indicate, the pope hopes will facilitate a negotiated settlement of the Polish crisis before there is more bloodshed.

In his "State of the Church" message, the pope, the former bishop of Krakow, said he was praying and appealing for "a peaceful solution" reached through "mutual collaboration between state authorities and citizens, in full respect for the civil, national, spiritual and religious identity of the nation."