Four suspected West German terrorists - two of them on the "most-wanted" list - have been arrested in Bulgaria and turned over to Bonn. It was the second time in less than a month that a Communist government in Eastern Europe has cooperated with West German security forces in capturing terrorists.

Last month, four others on Bonn's list were pinpointed in Zagreb, Yugoalavia, by traveling squads of German police and were arrested by Yugoslav authorities.

The latest catch may be an even more significant sign of improved international cooperation in the anti-terrorist battle because the Bulgarians apparently did not ask for anything in return and have already turned the suspects over to the West Germans.

The Yougoslavs still hold the other four terrorists and, although Bonn and Belgrade both officially deny it, the Yugoslavs seem clearly to intend to keep them until West Germany agrees to turn over a numner of anti-Yugoslav Croatian extremists in West German jails.

Bulgaria is the first Soviet-bloc country to cooperate openly with the West Germans in such matters, and officials here hope this is a sign that the Kremlin is not encouraging terrorists, as some Western intelligence agencies suspect.

The arrests in Bulgaria, which were made Wednesday and revealed yesterday by the Justice Ministry here, are also of great potential interest because one of those captured is Gabrielle Rollnick, 28.

She is believed to be a central link in an international chain of kidnaping and Italy.

Rollnick is wanted in Austria as a suspect in the kidnaping last November of textile magnate Walter Palmers, whose family paid almost $2 million for his release.

Austrian, West German, Italian and Swiss police have long suspected that the kidnaping was engineered by West German terrorists, mostly women, to fill the war chests of both the Red Army extremists of West Germany and the Red Brigades of Italy.

A former sociology student and daughter of a policeman, Rollnick was first arrested in September 1975 for alleged participation in the 1974 murder of a West Berlin judge and the 1975 kidnaping of a conservative political leader in West Berlin.

In mid-1976, she and three other women climbed out their prison windows on ropes and escaped. Also in jail with her before her escape and awaiting trial on the same murder and kidnap charges was terrorist, suspect Till Meyer.

Three weeks ago, four women got into the maximum security prison where Meyer, 34, was being held and freed Meyer and another alleged terrorist.

Rollnick is said by police to be one of those who helped free Meyer, and Meyer was one of the four captured in Bulgaria.

The two other suspects arrested in Bulgaria, both women, have not been identified publicly, but Bonn's new Interior minister, Gerhart Baum, indicated at a press conference yesterday that one of them is presumed to have been involved in the Palmers kidnaping.

He also indicated that Rollnick is linked to a Vienna apartment, uncovered a few days ago, that is believed to have been a hideout for hard-core West German terrorists.

Officials would not confirm or deny a published report that the apartment contained a "hit list" of West German political and military leaders who were to be assassinated.

Baum described the cooperation of Bulgarian authorities as "marvelous" and said the arrests were part of a joint operation involving special West German anti-terror squads, each assigned to tracking down individual terrorists.

The West Germans may have been very lucky.

Earlier today, a spokesman for West Berlin's Justice Ministry said Till Meyer had been spotted on a beach in Bulgaria by a West German prison officer who happened to be vacationing there.

Baum provided no details on how the four got to Bulgaria. There has always been concern that terrorists might escape through East Berlin, but Baum said East Germany had actually offered to help in the case.

Horst Herold, chief of West Germany's federal crime office, said yesterday that there is no evidence that Eastern Europe is a "logistical hinterland" for terrorists.

Although Western officials are still investigating possible Soviet and Czechoslovak support of terrorists, the cooperation of some in the East seems to reduce further the number of places where terrorists can find a haven.

The loss of potential sanctuary was first apparent last year after Palestinian extremists hijacked a Lufthansa airliner and the governments of Lebanon, Syria and Iraq refused to let them land. Vietnam and South Yemen would not agree to be part of a deal with them and Somalia allowed West German commandos to storm the plane.

Since Bonn launched a massive manhunt last fall after a year in which a chief federal prospecutor, a top bank official and an industrial leader were murdered, about 15 hardcore terrorists have been captured out of about 40 believed to be at large.

All were apprehended in other countries, where Baum says most of the terrorists are hiding. Of the 20 most wanted, five have now been caught, Baum said.

Baum said he would not comment officially on whether any conditions were attached to Bulgarian cooperation in the latest arrests, but none were apparent.

There is a growing awareness throughout most of the world, including Socialist states," Baum said, "that terrorism threatens our basic civilization."