A hijacker who demanded $3 million in cash, two machine guns, two parachutes and a reunion with an imprisoned friend held 13 hostages last night in a Frontier Airlines plane he commandeered in Nebraska and forced to fly to Atlanta.

Threatening that "a lot of people are going to suffer" if the demands were ignored, the hijacker let a 5 p.m. deadline pass, and an hour later released two women flight attendants.

The FBI identified the hijacker as Thomas Hannan, 29, of Grand Island, Neb., who was arrested last month after a $7,000 robbery at an Atlanta branch of a bank formerly headed by resigned Budget Director Bert Lance.

Hannan, who had been free on bond, included among his demands the release of his friend, George David Stewart, also 29, who has been in an Atlanta jail awaiting trial for the same robbery.

An FBI official in Atlanta said in a telephone interview last night that Stewart would be made available to talk with Hannan later in the evening.

The hijacker's parents flown to Atlanta from Grand Rapids, talked to their son over a control tower radio, after which Hannan was reported to have told authorities, "I need an honorable way out."

As negotiations dragged on through the afternoon, the FBI offered to give Hannan two parachutes in exchange for the two stewardesses still aboard the Boeing 737 jetliner.

The hijacker, carrying a sawed-off shotgun, pushed his way past a security guard at the Grand Island airport shortly after 6 a.m. and forced the pilot to take off. During a mid-morning refueling stop in Kansas City, the hijacker released 18 other hostages, including eight women and eight children, and ordered the plane flown to Atlanta.

The demand for the parachute indicated that Hannan might try to duplicate the sensational hijacking on Thanksgiving Eve, 1971, when D. B. Cooper bailed out of the tail door of a commandeered Boeing 727 jetliner over the Pacific Northwest with $200,000 in cash. He was never found.

However, Boeing officials in Seattle said it would be impossible for anyone to bail out of a 737 safely because the only doors are on the sides of the aircraft and a parachutist would be blown into the fuselage.

The motive for the hijacking became muddled last night amidst conflicting reports over an alleged homosexual relationship between Hannan and Stewart.

The Associated Press reported that the FBI had produced a circular describing the two as having a homosexual relationship. But FBI agents in Washington, Atlanta and Mobile, Ala., where the pair was arrested on the bank robbery charges, denied to The Washingon Post that any circular had been prepared much less one alleging homosexually.

United Press International reported that a 1973 Mobile police intelligence report indicated that the two met in Berkeley, Calif. last year and had been traveling around the country since. The UPI report said both admitted to having a homosexual relationship.

However, in a telephone interview, Detective Samuel McLarty, of the Mobile Police Department said he had no knowledge of such a report and would be surprised if one existed.

Police confirmed however, that Stewart, whose mother lives in Mobile, had been arrested there in 1973 on a charge of carrying a weapon without a permit. He reportedly was picked up wearing a Nazi-style uniform.

Authorities in Atlanta said Hannan and Stewart entered a National Bank of Georgia branch one morning in September, wearing khaki military-style uniforms and brandishing revolvers.

After forcing customers and employees to lie on the floor, they scooped uo $7,000 in cash and fled in a car.

They were taken into custody by FBI agents in Pritchard, Ala., near Mobile, on Sept. 3, police said.

The FBI reported that the pair had been accompanied from Atlanta by two 16-year old youths, who were not held.

Hannan, pleading a need to return to Grand Island to take care of personal business was released by a magistrate on $25,000 bond. Stewart, however, was held in the Fulton County Jail, near Atlanta.

There appeared to be little likelihood that authorities would attempt a commando-style assault on the hijacked airplane as was done earlier this week in Somalia, where three of four Arab and German hijackers wre killed.

Attorney General Griffin B. Bell said yesterday the FBI has special tactical teams trained to deal with hijackings, and an FBI spokesman said it is a "safe assumption" they had been alerted in the Atlanta case.

But such units have never been used, other than to position marksmen around a hijacked plane to be ready in the event of a deteriorating emergency situation.

Bell noted to reporters that federal law prohibits military units from rescuing hijacked aircraft in the United States.

The hijacking drama began when a man authorities identified as Hannan walked casually through a metal-detecting device at the small Grand Island airport, opened his carry-on suitcase for inspection and pulled from it a sawed-off shot gun.

After forcing an airport guard to back away from the ramp, Hannan then boarded the plane, which was scheduled for Denver with stops in Lincoln and Omaha.

After the plane landed in Kansas City and the 18 passengers were freed, it took off for the 600-mile trip to Atlanta. The aircraft landed there at noon, slightly behind schedule because of minor pressurization problems.

Meanwhile, Frontier Airlines officials made arrangements with Atlanta banks to package the ransom money, which was taken in an armored car to an FBI outpost a few hundred yards from where the hijacked plane was parked.

In mid-afternoon, the hijacker asked for - and received - 16 hamburgers, 16 milk shakes and two cartons of cigarettes.

As negotiations between FBI officials and Hannan continued through the afternoon by radio, Hannan said, "I was Stewart out of jail. I want him to come to this plane so I can talk to him . . . and the stewardesses can leave," UPI reported.

At that point, the wire service reported, FBI agent Donald Cochran told the hijacker, "If you want to see Stewart, we can arrange that. Just lay down your gun."

Shortly after that exchange, Stewart was flown from an undisclosed Atlanta location to the airfield in a helicopter, UPI reported.

For a while, the negotiations centered on the release of one stewardess, Bobbie Carr, the mother of a 4-year-old child, whom Hannan's father mentioned in one radio conversation with his son.

"I see the stewardess has a child she's worried about. Can you let her off?" the father was quoted as saying. "Your mother and I both think you ought to hand in that gun and call it quits. Can't you do that, boy?" the father said.

The two flight attendants walked off the plane a few minutes later.

As darkness fell at the Atlanta airport, the plane, its navigation lights flashing, was barely visible. There were no lights visible inside the plane and no floodlights. Traffic to other parts of the airport, away from the hijacked jet, continued. CAPTION: Picture 1, THOMAS HANNAN . . . had been free on bond; Picture 2, Two women flight attendants, with two unidentified men, leave the hijacked jetliner after being released. AP; Picture 3, GEORGE DAVID STEWART . . . flown to the airfield; Picture 4, An ambulance and armored truck, park at the Atlanta airport. UPI; Picture 5, It is not known if the truck contains $3 million the hijacker demanded. Left, a Kansas City worker delivers some papers. AP