Klaus Croissant, the West German lawyer who once lead the defense of the Baader-Meinhof terrorist gang, is today imprisoned in the same fortress-like jail at Stammheim that was specially designed to hold his former clients.

The lawyer, 47, who has never made any secret of his sympathies for the radical Red Army Faction of terrorists, was extradited last night from France where he had been under arrest on an international warrant issued by the Bonn government.

The irony of Croissant's present predicament is extraordinary. Yet there is much more to it than a turnabout in fortunes.

Croissant, perhaps more than any other figure linked to terrorism in West Germany, has come to symbolize the movement's cleverness, complexity and challenge to legal procedures.

Although Croissant stands accused and not convicted, West German authorities believe that the suite of law offices he ran with a dozen or so other radical lawyers on a Stuttgart sidestreet was a hub tied to virtually every major German terrorist crime of recent years.

For example, police believe that Hans-Joachim Klein, a one-time messenger and driver for Croissant's firm, was among those who raided the oil exporters' conference in Vienna in December 1975. Klein has since disappeared.

Siegfried Hausner reportedly joined the firm as a clerk in December 1974 and four months later died during an attack on the West German embassy in Stockholm.

Willy Peter Stoll, alleged to have been an assistant to Croissant, is a suspect in connection with three killings in the last seven months that have stunned West Germany - the murders of chief federal prosecutor Seigfried Buback in April, Dresdner Bank president Juergen Ponto in July and industrial leader Hanns-Martin Svcheyer in October.

A prime suspect in the Ponto case is the banker's goddaughter, Susanne Albrecht, who is alleged to have been a former law office assistant and was observed with Croissant on the defense bench in Stockholm.

Silke Mayer-Witt, another former assistant, is also wanted in the Ponto case and in the attempted rocket attack a few months ago on the federal prosecutor's building.

Angelika Speitel, who worked for Croissant until the end of last year and then went underground, is wanted in connection with the Buback slaying.

Croissant, like many of those linked with West Germany's ultra-left extremists, comes from comfortable surroundings. The son of a well-to-do drugstore owner, Croissant was a successful lawyer specializing in divorce and inheritance cases. Like a number of other young lawyers at the time, his outlook changed the student radical movements of the late 1960s.

He became a partner of Jorg Lang, who disappeared in 1974 before he was to go trial for alllegedly recruiting helpers for the Baader-Meinhof group.

In addtion to allegations by the Justice Ministry of harboring members of a criminal organization, Croissant is accused of masterminding a message-smuggling operation between prisoners and their comrades on the outside that essentially allowed the Baader-Meinhof leaders to continue their operations from a jail cell.

Croissant says he is not terrorist but supports the Red Army faction because it is fighting against a West German "regime that has already entered into a disguised fascism."

Indeed, an objective of the faction has been, aside from overturning the West German government, to provoke the authorities into overraction that would make Croissant' description seem accurate.

The government - mindful of the past and the ease with which many people believe the worst about Germany - has been trying to find a strong yet constitutional means to deal with terrorism.

Constitution and court procedures here generally are liberal. Accused terrorists and their lawyers frequently have touched off disruptions in the courtroom for which there is no prescibed response and have provoked some judges into indiscretions.

It is the combination of clever terrorists and clever lawyers, working within a country inhibited by its past yet traditionally prone to overreaction, that produces West Germany's unusual problem.

Croissant had been charged earlier this year on conspiracy and subversion counts. He was released on $35,000 bail and told not to leave the country.

In July, however, he fled to France, first seeking political asylum and then going underground.

The decision of a Paris court to approve extradition is welcomed here as signal that other countries will not accept political justifications for murders.

Stammheim is the prison where just a few weeks ago the three surviving leaders of the Baader-Meinhof gang - including co-founder Andreas Baader - commited suicide just hours after a West German commando team overwhelmed the hijackers of a Lufthansa jet in Somalia.

An internationally supervised autopsy confirmed the deaths as suicide. German officials say the prisoners, true to their efforts to disparage the state, tried to make it look like murder.

Croissant and others say it was murder and today, in a letter published in a Paris paper, Croissant said, "If you ever hear of my death in a German prison, it will not be suicide."