The Red Brigades kidnapers holding U.S. Gen. James L. Dozier prisoner released their fifth communique on the abduction today with a Polaroid snapshot indicating that the general, now heavily bearded, may still be alive.

Today's message, found in a downtown trash can after an anonymous caller tipped off a Rome newspaper, was the first since Jan. 16 and the fifth since Dozier, deputy commander of the NATO military base at Verona, was kidnaped 39 days ago by a group of people disguised as plumbers. The radical Red Brigades later claimed responsibility for the abduction.

Today's six-page communique was quickly confiscated by police. Editors at the Rome daily, Il Giornale d'Italia, said it contained anti-NATO and anti-American statements but made no demands for Dozier's release and made no mention of a sentence having been reached in his so-called people's trial.

The comunique did, however, rule out the prospect of negotiations.

"Negotiate? Whatever for? The proletariat has nothing to negotiate with the bourgeoisie," it said in part.

The picture included with the message, the second his captors have circulated, reportedly shows the usually clean-shaven general holding up a sign reading "the capitalist crisis generates imperialist war."

Yesterday, police in Rome found a cassette with a taped message criticizing Dozier and his role in NATO, but investigators say the recorded message provided no new evidence that could help them discover where Dozier is being held.

Interior Minister Virginio Rognoni admitted yesterday that a five-week search had turned up few clues to the 50 year-old general's whereabouts.

Investigators have expressed some perplexity about the nature of the Dozier kidnaping, since it appears to be proceeding at a different rhythm than most of the Red Brigades' previous abductions. They point out that the communiques have been few and far between, that there have been no demands, no letters from the victim, and that the language of the communiques released so far contains relatively few concrete references to Dozier.

Some observers here have suggested that Dozier may have been taken out of the country, but Italian police speculate instead that the dearth of communications reflects the inhibiting effect on the kidnapers of the massive police search still under way in much of northern Italy. They also believe that the Red Brigades may be holding Dozier in the same still-undiscovered hideout they used last summer when they kidnaped petrochemical executive Giuseppe Taliercio, murdered after 47 days in captivity.

In Taliercio's case there also were no demands and only one letter. After his death police officials said this might have reflected his refusal to cooperate.

The anomalies in the case, combined with recent trips by Mrs. Dozier to the NATO military headquarters and then to West Germany, have led to unsubstantiated press speculation that contact with the kidnapers may have been made or that Dozier may now be in the hands of "foreign intelligence agents." But police say they believe Dozier is still in the hands of his original kidnapers.