The hijacking of a Luftansa jet with 91 persons aboard has plunged the West German government into a grave crisis in which it must decide before Sunday morning whether to release 11 jailed members of a notorious terrorist gang or risk the death of all the plane's passengers and a leading industrialist kidnapped 40 days ago.

Though the Bonn government had managed to negotiate a stand-off since Sept. 5 with the kidnappers of Hanns-Martin Schleyer, the hijacking by a group allied with the kidnappers has put a vastly more powerful bargaining weapon in the hands of theterrorist groups seeking to free their jailed associates.

Ultimatums and photographs delivered to the Bonn government today and distributed to several French and German newspapers made it clear that the two groups are acting in unison.

The ultimatum to West German Chancellor Helmut Schmidt from the "Siegfried Hausner group of the Red Army faction." the group that kidnapped Schleyer, said the passengers and crew of the capturedairliner were "completelyunder our control."

Schleyer, who is being held in an undisclosed location, and the passengers and crew of the hijacked Boeing 737 jet - which is now in Dubai at the top of the Persian Gulf - will be "killed immediately," the statement said. "If the prisoner are not released or do not reach their destinations, and if the money is not delivered in the way and at the time requested."

Similar ultimatums were delivered by the airplane hijackers who call themselves the "Organization of Struggle Against World Imperialism."

The ultimatums demand that all prisoners must reach their destinations - either South Yemen, Vietnam or Somalia - by 8 a.m. Sunday GMT 2 p.m. EDT.

There has never been any public indication that those countries would receive released terrorists.

The 11 in West German jails are six men and five women, including two of the surviving leaders of the Baader-Meinhof urban guerrila gang - Andreas Baader and Gudrun Ensslin.The hijackers have also demanded release of two Palestinian prisoners in a Turkish jail. Turkey has flatly refused the request.

The hijacking of the jet yesterday afternoon over the Mediterranean after it took off from the Spanish island of Malloreor humiliation for German police. Security especially atairports serving Lufthansa, has been very heavy since theSchleyer kidnapping, which came after a wave of terroristkillings.

While Schmidt and a special crisis staff of leaders of all political parties agonized in Bonn, the twin-engine Lufthansa jet stood in aremote corner of the Dunbai airport, some 4,000 miles away, with all aboard sweltering in 95-degree heat.

There are believed to be 86 passengers - including nine women and six children - and fivecrew members aboard the plane.

Bonn government spokesmanKlaus Boelling said today there are believed to be four hijackers - two men and two women- armed with guns and hand grenades. The official news agency in the United Arab Emirates, at the southern tip of the Persian Gulf, said it was uncertain how many hijackers were aboard, although Dunbai officials said there appeared to be two who spoke Arabic.

Hough numerous deadlines have gone by without incident in the stand-off between Bonn and the Schleyer Kidnappers, the ultimatums todaysaid "this is our final contact with you." Boelling madeit clear that the government was viewing the situation "very, very seriously."

Aside from the release of jailed terrorists, the hijackers and kidnappers are demanding the equivalent of $15 million in ransom.

The deepening of thecrisis developed slowly here because Bonn was not sure until the early hours of the morning, that the hijacking was linked to the Schleyer kidnapping.

Bonn officials were in continuous radio contact with the jet - which made refueling stops in Rome on Cyprus and in Baharain.

Boelling disclosed that another jet carrying special anti-terrorist police units trailed the hijacked plane in case the government in whatever country the 737 landed in requested forces for a rescue attempt.

There was no indication where that flying police unit is now.

At Dubai, West German Ambassador Joachim Neumann and the defense minister of the united Arab Emirate, Sheikh Mohammed Bin Rashed Maktum, were reportedly trying to negotiate with the hijackers to release the women and children.

Food, water and an air conditioner reportedly were brought aboard the airliner at Durbai.

Boelling also said that a representive of the Palestine Ligeration Organization, which has disclaimed any connection with the hijacking, tried unsuccessfully to bargain with the terrorists during the brief stopover in Cyprus.

In the ultimatum delivered to Bonn, the terrorist said: "We have left Helmut Schmidt enough time to make his decision between the American strategy of destroying the liberation movements of Western Europe and the Third World and the interests of the government which are not to sacrifice the man (Schleyer) who is for them the most important economic magnate for the sake of this imperialist strategy."

The reference to "American strategy" injected a new element into the tactics of the terrorists.

It was the first time in a long while that a major terrorist statement has prominently mentioned the United States. Though in the late 1960s and early 1970s, the Baader-Meinhof gang used the Vietnam war as an excuse for numerousurban guerrila bombings, their successors have since thenfocused almost exclusively on attackings West German society.

This is the fourth hijacking of a Lufthansa jet andin all previous cases the hijackers have received something for their efforts.

In February, 1972, Bonn paid a ransom to hijackers. In October that same year, terrorists grabbed another Lufthansa jet and traded it for release of three Arabs held in the attack on Israeli athletes at Munich. In February, 1973, another guerrilla band commandeered a plane to fly them from Rome to Kuwait after carrying out a bomb attack on a Pan American jet