Penne Laingen was not far from the phone when it rang yesterday morning in her Bethesda home. It was her husband, Bruce -- the top American diplomat in Tehran -- calling from his enforced captivity in the Iranian Foreign Ministry.

"He told me today that the morale (of the 49 U.S. hostages) was very high -- that they were strong from top to bottom," Mrs. Laingen said. "He said that they have a spirit of togetherness that is going to carry them through."

Mrs. Laingen frequently telephones the families of other U.S. hostages, passing along the encouraging words from her husband to wives and mothers becoming discouraged as their vigil moves into its fourth week.

The only thing that keeps these reports from being even more reassuring is the knowledge that Bruce Laingen, the U.S. charge d'affaires in Tehran is, like the rest of America, receiving his information about the hostages secondhand.

He is not confined with the 49 hostages at the U.S. Embassy. He is instead held in protective custody by the Iranian government at the Foreign Ministry, and is not allowed to contact the hostages directly.

He spends his days, Mrs. Laingen said, attempting to negotiate on behalf of his captured staff with "anyone will come to see him."

And when he can, he calls his wife and tries to pass along the messages of hope that she in turn relays across the United States.

"The only message I can pass along to the others is my husband saying, 'I worked with this guy, and he is tough,'" Penne Laingen said.

"I am on the phone constantly, daily, to a number of the families, the ones I know need help," she said. "We just jack each other up. When we first met President Carter at the State Department, we were strangers, but now ours is a fraternity that will be lifelong. It's a gut family relationship."

"My husband's spirits are still very high," Mrs. Laingen said. "He's tired, and he's getting a little cold -- it's starting to get cold in Iran. I think the one thing that bothers him most is that he doesn't know much about the others, and he looks on them as a family. But he's confident."

On Thursday, Bruce Laingen sent a Thanksgiving message through his wife and the State Department, asking that the nation's church bells ring each day in hope of "the restoration of the traditional friendship between the American and the Iranian people."

For the Laingens, who have spent much of their adult lives as representatives of America in Middle Eastern countries, it is the sudden outpouring of anti-American feeling that hurts the most.

"It's a very bitter pill for me to see the demonstrations," said Penne Laingen, who spent four years in Pakistan and three years in Afghanistan with her husband.

"I don't know much about money matters or power plays," she said. "But I do know how Bruce and I have spent our lives trying to project a good neighbor image for America.

"We have devoted our lives to giving, giving, giving in these countries. The problem was that we were always looked upon as the rich Americans. And to come back from that and suddenly be called an ugly American, and all this talk about Bruce being prosecuted for espionage -- it really hurts. It's a lifetime down the drain."

Bruce Laingen, she said, "really loves Iran. It's such a shame that he has not been given a chance to have an audience with the ayatollah and get across what he was trying to do, which is work within the revolutionary system.

"They can't win this way and they may lose the revolution by doing it."

Although the long crisis has made her bitter, Penne Laingen said her support for the American position has not weakened.

"I have faith that they all will be released and that Bruce will be released when the ardor and the fervor of the revolution has died down," she said. "I know that somewhere in Iran, there is someone with reason who must get to Khomeini and say, 'We must get out of this.' That's what I pray will happen -- that reason will prevail."

In the meantime, Mrs. Laingen says, she is calling and calling -- and praying.

"It's tragic for all the little people who have spent their lives trying to help in foreign countries," she said. "With Vietnam and Watergate, it seems we just lost our faith, our hope. But maybe now we'll get it back." CAPTION: Picture, BRUCE LAINGEN . . . U.S. charge d'affaires in Iran