Students and teachers at Warsaw University interrupted lectures for 15 minutes today and signed petitions to protest the dismissal by martial-law authorities of their democratically elected rector.

The protests, which were calm and orderly, reflected the depth of feeling at the university to the removal last week of Prof. Henryk Samsonowicz and the resignation of his three deputies. But there were differences of opinion about whether the removal signaled the start of a general purge of academic life.

A measure of the complex political situation here four months after the imposition of martial law came in a conciliatory-sounding statement issued Wednesday night by the Politburo of the Communist Party. The statement said that "the progressive stabilization in the country creates good conditions for the implementation of the line of agreement" between the government and society.

The Politburo added, however, that there were still "destructive forces" opposing national reconciliation and intent on sowing unrest.

The significance of the Politburo statement is that, by putting the emphasis on life returning to normal, it could prepare the ground for possible negotiations with the Roman Catholic Church and the suspended Solidarity trade union. Further evidence of the party's intentions is likely to be provided by a meeting of its policy-making Central Committee announced for April 22.

The somewhat contradictory political signals emerging from Warsaw are taken here as evidence that the military leadership under Gen. Wojciech Jaruzelski still has no clear vision of the way ahead. Many decisions, including the shake-up at Warsaw University, appear to be the result of the day-to-day political power play rather than a conscious strategy worked out by the rulers.

Most political analysts think Jaruzelski would like to reach an understanding with the church and trade unions, as long as the party's supremacy is assured. There is, however, an enormous--and perhaps unbridgeable--gap between the two sides in their conception of what this new agreement should consist of.

Samsonowicz's dismissal has further alienated the intellectual community, many of whom are refusing to cooperate with the government in any way. A prominent professor of medieval history, Samsonowicz was regarded buy many as a skilled diplomat who defused conflicts at the university and was popular among both students and staff.

After the imposition of martial law, he called for the release of about 25 university members who had been interned. Along with other university rectors, he also refused to dismiss teachers for their political or ideological views.

University sources said that his replacement, Prof. Kazimierz Dobrowolski, was largely unknown, although he had served for three years as a deputy rector in the late 1970s. He reportedly is receiving little cooperation from the university staff and has so far been unable to find suitable candidates to fill the three vacant deputy rector posts.

Fourteen of 18 department heads have signed a petition, addressed to the minister of education, calling for Samsonowicz's reinstatement. The petition said that since he had been elected, his removal violated the principles of free academic life including "truth, pluralism, tolerance and the rule of law."

Students and teachers at several university departments staged a symbolic, 15-minute strike at noon today and signed the petition. Classes in other departments were not interrupted, but students said they supported the protest.

Until now, martial law has had little effect on academic life in Poland. It has led to tighter discipline for students, including obligatory attendance at lectures, but teachers say that in Warsaw at least there has been no attempt to interfere with the content of lectures.

If authorities decided to get tough with the universities, few lecturers think there would be much effective resistance.

"All they would have to do is get rid of 20 percent of the staff and 10 percent of the students, and everybody else would be frightened into obedience. But that would destroy Jaruzelski's hopes for a national agreement," a staff member said.