With less than a month to go before the formal opening here of a second East-West conference to review the progress of detente under the Helsinki accords, Western delegates attending preparatory meetings express concern that Soviet stonewalling could force the 35 nations of the Conference on Security and Cooperation in Europe into the main sessions without an agreed agenda.

Five weeks after the preparatory meetings opened Sept. 9, the two blocs maintain adamantly opposed positions on the key agenda issue: how much time should be set aside at the main meeting, opening Nov. 11, for debate on the implementation of the human rights accords that were enshrined in the final act of the 1975 conference on detente held in Helsinki, Finland.

Reflecting an exasperation generally shared among all but the Eastern Bloc delegations, the U.S. group's co-chairman, Max Kampelman, told a preparatory plenary session today that his delegation believed "a mutuality of constructive attitudes is missing here."

The agenda deadlock set in when East Germany proposed last Friday a Soviet-backed agenda timetable that would drastically reduce discussion on the human rights issues that the West says is all-important in this second followup to Helsinki.

This preliminary stage of the conference is paralyzed by Western insistence on a thorough exchange of views on the highly controversial subjects of Afghanistan and the treatment of dissidents and by the corresponding Soviet Bloc position that discussion on sensitive subjects should be kept at a minimum.

A U.S. spokesman labeled the East German agenda proposal "totally unacceptable" while another Western conference source said it "could not be taken seriously." U.S. Ambassador Kampelman alluded to the East German proposal today, saying that "our willingness to seek a constructive compromise has been met by a persistent, stubborn and relentless pursuit of a proposal that has little support."

Lined up against the Eastern position are 28 of the 35 delegations. The 28 are insisting on six weeks to review implementation of the Helsinki agreements. The East German proposal, which is staunchly backed by the Soviets, could reduce the rights debate to 2 1/2 days, according to Western sources.

Accusations of Soviet "stonewalling" have been freely leveled by the Western and nonaligned groups. The latter appears to have joined forces with the NATO bloc in the attempt to ensure that the conference has timie to review implementation of promises made at Helsinki. Last week, Kampelman accused the East of desiring to "cripple the implementation review."

Kampelman is to leave for Washington Friday for personal engagements.

Before the preliminaries opened last month, it had been understood that all delegations would adhere broadly to the agenda ground rules laid down in the last Helsinki review conference held in Belgrade in 1977-1978. Kampelman had said he expected the preparatory conference to last "days rather than weeks."

Eastern Bloc sources said, however, that it was "unrealistic" of the West to expect the Soviet Bloc to accept automatically the same framework for the Madrid conference and thereby to submit to a repeat of the frontal criticism that occurred in Belgrade when the then U.S. delegation chief Arthur Goldberg championed the human rights issue. The Belgrade conference ended with few formal commitments other than to meet again in Madrid next month.

The Western Bloc and the nonaligned nations have broadly backed an initial timetable proposal put forward by host Spain that is closely modeled on the Belgrade approach to the agenda issue.

Speculating on the continuation of the current deadlock and the possibility that there might be no formal agenda agreement by Nov. 11, one Western source said a conceivable scenario was that Spain, as host, would take the chair and that then "each delegation would raise their hands and speak in turn."