They have experienced a terror most Americans will never face. The fear can be so overwhelming, says psychiatrist Martin Symonds, that "you forget everything you ever learned."

Specialists on the effects of terrorism agree that the 39 Americans taken hostage in the hijacking of TWA Flight 847 two weeks ago are angry, scared and feeling helpless -- the very emotions that can bind hostage to captor in what doctors call the Stockholm syndrome.

The name is taken from an incident in which a woman held hostage by robbers in a Stockholm bank vault later married one of her captors.

The hostages see their problem "through the eyes of the terrorist," said Dr. Steve R. Pieczenik, a psychiatrist and an assistant secretary of state during the Iranian hostage crisis that ended in 1981. Pieczenik said he would be surprised if the TWA hostages were not angry at the United States and at Israel, which refused to meet the hijackers' demand to release more than 700 Lebanese prisoners, mostly Shiites.

"That doesn't make them traitors . . . ," he said of the hostages. "That's survival . . . . You begin to think that way."

Interviews with some of the hostages broadcast on American television yesterday evening seemed to confirm some of Pieczenik's predictions. Several of the captive Americans said they were angry and frustrated, and several spoke sympathetically of their captors' demands. Allyn Conwell, spokesman for the group, for example, endorsed his captors' demand that Israel release the Lebanese prisoners.

Another hostage, Thomas W. Murry, said in an ABC broadcast: "I really feel that my being taken hostage was a way that the people here had . . . to point out that there are hostages in Israel."

According to Symonds, a member of the American Psychiatric Association's Task Force on Terrorism and Its Effect on Victims, a hostage will "try to relate to the person that has complete control" over his life. In reality, Symonds said, "You are just merchandise to the taker. He keeps you under the illusion that you are alive and well. At this point the victim starts to think that the guy that has him is not at fault, so he feels that the danger is from the outside."

Therefore, Symonds said, the hostages are likely to direct their anger "at the people who won't give the takers what they want. They see that the only thing that is holding them up is price."

This bond between hostage and captors, specialists agree, can lead the hostage to say publicly that he is being treated well even though he is not, as happened when the Americans were held hostage for 444 days at the U.S. Embassy in Iran. Some were quoted as saying their treatment was not that bad, although they were often kept in darkened rooms, restricted from conversations with their fellow hostages and deprived of sleep.

Pieczenik says he has been skeptical about the TWA hostages' statements during well-staged news conferences. "Their survival is at issue, and the well-being of the other hostages," Pieczenik said.

He added that the news media play an important role -- during captivity and afterward. "While they are hostages they want the media attention because it gives the hostage . . . some leverage over the U.S. government and the decisions affecting their lives," he said. But he cautioned that constant media attention loses its therapeutic value. According to Symonds, the former hostage feels used after the story fades from newspapers and broadcasts.

Dr. Eric Plaut, vice chairman of Psychiatry at Northwestern University, said statements by Conwell and others could indicate that the captives had psychologically identified with their captors or could be "just a carefully prepared statement" written by the captors.

After they are released, Symonds said, some hostages become depressed -- and their attitudes and outlook on life are likely to change.

"I tell people that were held hostage that they got a second life, and opportunity to reassess," he said. He urges hostages' families and friends to help them by giving them back their sense of power. He said his recommendation when the hostages were returned from Iran was to give them a buffet dinner and allow them to choose what they wanted to eat. "Giving them decision-making power makes them human again," he said.