The arrest in a Paris apartment last month of two West German terrorist suspects and their three roommates revealed preparations for several planned attacks in West Germany.

The evidence triggered a police search through towns in southwest Germany, where other urban guerrillas were believed by police to be in hiding. But none was found.

Although there has not been a major terrorist action in West Germany for three years, police officials have warned periodically that "something is in preparation." This ominous drum roll appears intended partly to maintain public vigilance and to ensure continued support for the state's own occasionally overly enthusiastic law-enforcement efforts.

But this year the concern seems particularly acute. The worry is that a wave of terrorist strikes this summer or in early autumn could gravely damage the Bonn government by embarrassing Chancellor Helmut Schmidt, facing an October election, and bring to power his opponent, conservative Bavarian Minister Franz Josep Strauss. The left-wing extremists favor Strauss because, in their view, his hard-line politics would precipiate just the sort of reaction against terrorism that could topple the current system.

"If terrorists want to hurt Schmidt, now would be the time to strike," said one of his aides. "Two things could topple Schmidt. One is the Soviets, and he is managing that aspect well. The other is a resurgence of terrorism."

Such angst was pigued last month by two unexpected and unusually violent protest actions in Bremen and West Berlin. The demonstrators deepened the furrows on Bonn brows by suggesting that West German radicals might still be able to muster a community of sympathizers, although a much smaller one.

The Bremen protest was against a ceremonial swearing-in of 1,200 Army recruits, marking the 25th anniversary of West Germany's membership in NATO. More than 250 policemen and soldiers were injured in a stormy battle with at least 3,000 demonstrators. It was the most violent display of antimilitary sentiment here since the 1950s protests against rearmament.

Less than two weeks later in West Berlin, a group of 200 leftists fought with police, ransacked the Amerika House cultural center and set fire to an American flag. The Bonn government condemned both incidents.

German specialists on terrorism see differences between last month's violence and the 1960s protest actions that gave shelter and inspiration to West Germany's early terrorist movement. The recent flare-ups were said to be not student revolts but the work of committed, left-wing rabble-rousers, lacking the ideological foundations of the youth movement a decade ago.

"I do not think terrorism will come again in the same form," said Friedhelm Neidhardt, a professor of sociology at the University of Cologne and an expert on terrorism. "I think terrorism has been a disppointment for those who thought it would be an instrument to change the world. They did not get the change. Now they have lose their supporters and their leaders."

The wanted posters still hang in public buildings, with mug shots of those most sought. Bonn resembles an armed camp in some areas, with government buildings surrounded by barbed wire and armored police cars patrolling the streets. But the general alarm on terrorism has faded.

Both the public's obsession with fighting terrorists, and media reports on their roots in the coldness, materialism and rigidity of affluent West German society are nearly gone.

The peak of terrorist activity came in 1977, when members of the Red Army Faction murdered the federal attorney general, a bank president and the president of the national employers' association. They also participated in a plane hijacking that eventually led to the mysterious suicides of Andreas Baader, the group's leader, and two associates in their prison cells.

According to estimates given by the federal prosecutor's office in Karlsruhe, there are 15 hard-core terrorists among 37 persons being sought for terrorist activities, and anywhere from 100 several hundred in a second circle of supporters.

More German terrorists are thought by police to be living outside the country than inside, mainly in the Middle East. It was a tip from a source there that reportedly led to the recent Paris arrests.

Improved international police cooperation in part explains the success at halting terrorist acts here, involving a pool of personal data on suspects in a computer at Wiesbaden. Even communist East European authorities cooperate.

"There is certainly still a potential for terrorism among young men and women who cannot see roles for themselves and are dissatisfied," said Neidhardt, but there are more alternatives to terrorism.

"Some are choosing to withdraw through drugs or religious sects. Others are joining communist groups, which are more developed now. These groups are highly disciplined, but don't see terrorism as a political method. They are prone to violence, motivated to irritate and demonstrate, but not to terrorize.

"The change," added Neidhadt, "is not that more young people are conformists and that life is now okay. The scene here is not more comfortable. German students are still highly frustrated. But they don't know how to change things. I see in many of them a quiet, fatalistic attitude. Also, they are very worried about finding jobs."