President Reagan welcomed 30 Americans back to the United States from their ordeal in Lebanon yesterday with a joyful reunion ceremony tempered by a vow that "there will be no forgetting" the murder of Navy diver Robert Dean Stethem and the seven hostages left behind in Lebanon.

On a day that alternated between scenes of grief and happiness, Reagan laid a wreath at Stethem's grave at Arlington National Cemetery and later told the former hostages, "This is one sad note today, and there are seven other sad notes, and we're going to continue to work on that."

The 30 former captives and their families emerged from the plane at Andrews Air Force Base looking like almost any group of travelers returning from a European jaunt. Red Trans World Airlines flight bags were slung over their shoulders, their eyes searched out relatives and friends in the crowd and their huge smiles said they were glad to be home.

Nine other passengers from TWA Flight 847, hijacked June 14, were returning separately.

"I'm going to hug my family, say hello to my friends, order a pizza and drink a pitcher of beer," said a beaming Robert Peel Jr., 33, a father of three from Hutchinson, Kan. He was accompanied by his wife, Kristi, one of the original hostages, who flew to Frankfurt to meet him Sunday.

Several of the nine who returned independently from West Germany expressed venomous anger, earlier suppressed, toward their captors. Arthur Toga, 33, a St. Louis professor of neurology, told ABC News that he was forced by a Shiite guard to play Russian roulette, with a pistol pointed at his stomach.

In brief remarks to the former hostages, families and hundreds of military personnel at Andrews yesterday, Reagan said, "There's only one thing to say, and I say it from the bottom of my heart in the name of all the people of our country: Welcome home."

Reagan also said, "There are promises to be kept. The day your plane was hijacked, the terrorists focused their brutality on a brave young man who was a member of the armed forces of the United States. They beat Robbie Stethem without mercy, then shot him to death.

"I know you care deeply about Robbie Stethem and what was done to him. We will not forget what was done to him. There will be no forgetting. His murderers must be brought to justice."

White House spokesman Larry Speakes announced that the United States will use "whatever steps are available to us," both "judicial and otherwise," to "bring these people to justice." State Department spokesman Bernard Kalb said the United States will seek extradition of the hijackers from Lebanon under international treaties.

"Should our diplomatic efforts fail, we at least have laid a basis for further unilateral efforts in appropriate circumstances," Kalb said, refusing to elaborate.

Transportation Secretary Elizabeth Hanford Dole issued an order yesterday prohibiting sales in the United States of tickets involving air service to Lebanon.

As the hostages were flying here from Frankfurt yesterday, Reagan telephoned Stethem's brother, Patrick, at his home in Waldorf, Md. The president acknowledged that it was a difficult time as the other former hostages returned home and told Stethem that the nation respects the murdered Navy diver as "an American hero."

Stethem was killed by Shiite Moslem hijackers after they diverted Flight 847 shortly after leaving Athens.

Later yesterday, the president and Nancy Reagan laid wreaths of red and white carnations and roses at Stethem's grave. They were joined by Stethem's sister, Sherry Sierralta, who dabbed at tears with a handkerchief in a brief ceremony at the cemetery.

At Andrews, about 400 well-wishers gathered spontaneously, reflecting the national empathy with and unease about the plight of the hostages and their families. It was not that these people were heroes, the welcomers said; it was more a realization that this could have happened to any of them.

Members of the group waved American flags, wore yellow ribbons and held signs saying "Thank you Ron and Nancy" and "USA is No. 1." The signs were distributed as the well-wishers passed through metal detectors. At least one was original: "Louisiana Loves Steve Willett . . . plus the 38."

Lois Gouaux and two companions who held the sign said they had driven for three days from Choupic, La., Willett's hometown, to greet their friend and fellow Roman Catholic Church parishioner. "We were scared for him, we were worried for him, and now we are thrilled for him," Gouaux said.

The former hostages reached American soil at 3:28 p.m., when their TWA L1011 jumbo jet touched down under glaring sunshine after a flight from Frankfurt. One woman on the plane was reading a Bible as the Reagans boarded amid long applause to deliver the official welcome.

"Folks, let me take you back here. I want you to meet some good friends of mine," John L. Testrake, pilot of the hijacked plane, said to the Reagans as he led them to the cabin.

On the flight home, Testrake, 58, was chosen to read a statement on the returnees' behalf. White House officials said they welcomed that because of concern about some statements by Allyn Conwell, the former hostages' spokesman.

"I didn't know there was controversy surrounding me acting as spokesman," Conwell said yesterday. "I'm aware of . . . controversy in regard to interpretation of some of the statements I've made."

Another returnee, the Rev. James McLoughlin of Geneva, Ill., praised Conwell and said "there wasn't any decision" to replace him as spokesman.

Testrake disembarked first. As each other returning hostage emerged, relatives in the crowd yelped, waved their arms in huge arcs and jumped for joy.

Victor Amburgy, 31, of San Francisco, raised his hands over his head, and several of his waiting relatives cheered and did the same when they spotted him. He embraced his roommate and fellow hostage, John McCarty, 40, and the two descended the stairs together as if in a triumphal march.

Not all of the former hostages chose to return to the pomp and circumstance of Andrews, and some of them expressed distaste for the ceremony.

Peter Hill, 57, of Hoffman Estates, Ill., said he chose to return home Monday night, apart from the group, because "some former hostages felt a bizarre allegiance to the terrorists . . . . It made me vomit. I would have spit in their faces." Hill was referring to statements, such as several by Conwell and others, praising the Amal militia for kind treatment and expressing sympathy with the Amal cause.

Several returning hostages bared previously unexpressed anger toward their captors.

"The people who took us off the plane are vile, disgusting animals," said Richard Herzberg, 33, an insurance salesman from Norfolk, Va., who was returning from a honeymoon with his wife, Sue Ellen, when the plane was hijacked.

Herzberg, one of four passengers with "Jewish-sounding names" who were held separately by the more radical Hezbollah Shiite faction, said the hijacker who killed Stethem threatened Herzberg during his captivity in Beirut.

" The hijacker comes into our room four days ago brandishing the same gun he had on the plane," Herzberg told CBS Morning News. "He goes: 'Do you know me?' And when we said no, he pulls out a 9-mm chrome-plated gun and says, 'You know me.' "

The FBI debriefed the former captives, and Toga said he was asked if he could identify Stethem's killers -- the original hijackers -- from pictures. "I will never forget their faces -- never," he told NBC.

At a news conference in Norfolk, five Navy divers who were among the hostages indicated that they had plotted to escape but never got the opportunity, Knight-Ridder reported.

"We had a plan to get away, but there was no way," said Petty Officer 3rd Class Kenneth Owen. "We felt if we could make it to the ocean, we could swim out, and then swim south."

"We were always thinking in terms of an escape plan," added Petty Officer 1st Class Stuart Dahl.

Although most of the returnees at Andrews expressed only relief, some indicated little sympathy for their captors. They applauded with feeling when Reagan said "these murderers will be brought to justice." Testrake, reading the hostages' statement, asked Reagan to obtain the release of seven Americans still captive "very soon."

Testrake voiced "our sincere respect and gratitude to President Reagan and the United States government" for helping to bring about the release. He said that public support "gave us the courage and strength to withstand in the darkest times" but that the real credit goes to "our Father, God."

After a 30-minute ceremony, the Air Force Band struck up "Stars and Stripes Forever," and many former hostages embraced as they prepared to separate after 18 days. As they filed out with their families, many people reached from the crowd to shake their hands.

One handed a small American flag to Grant Elliott, 33, a factory worker from Algonquin, Ill. He took it with enthusiasm, holding it high above his head as he walked out with cousins and his grandmother, Barbara Elliott, who had come from Connecticut to meet him.

Like travelers trying to make connections anywhere, the hostages quickly scattered after the ceremony -- some in vans provided by TWA for connecting flights from area airports, others in cabs.

Many of the hostages appeared talked out. Asked what he planned to do on arriving home in Boston, Stuart Darsch, who celebrated his 30th birthday on the day of his release, said only: "Sleep."

Peel, sporting a brown cloth hat and plaid shirt, told relatives that he went through three stages while in captivity: "the first three days were terror and then boredom and then it just became comical." He said a fellow hostage, upon being given his luggage, put on his wife's shirts and modeled them for the others.

As Peel stepped into a taxi with his wife, he was asked how he would travel home to Kansas. Smiling broadly, he said: "Unfortunately, fly."