From Denver and Milwaukee, St. Louis and Little Rock, from all over the nation, families of the 50 hostages held in Iran came to Washington yesterday to comfort and be comforted.

They heard what they already knew:

That their brothers, sisters, husbands, wives and children are still prisoners in a far-off land, surrounded by armed guards and mobs chanting slogans of revenge.

But they talked to President Carter and Secretary of State Cyrus R. Vance and, after the daylong briefings and many conversations in the marble corridors of the State Department, they at last knew they were not alone in their grief.

Walking toward the department cafeteria with some other relatives of the American hostages, Betty Kirtly of Little Rock could not hold back her tears. Her son, Steven, a Marine sergeant, is a hostage, "but I don't feel so bad knowing that other people feel the way I do." she said.

In a statement drafted by Penne Laingen, whose husband, Bruce, is the U.S. charge d'affaires in Tehran but is not one of those being held in the U.S. Embassy compound, the families asked that Americans send postcards and petitions to the Iranian Embassy here, reading: "To the Iranian people: the American people ask that the hostages be freed immediately."

The statement read: "Those we love are being held hostage in Iran. We wish to speak with one voice on behalf of all of them in thanking you, the American people, for your strong, steady and calm support during the last few weeks . . . This is just a simple human plea for the release of fellow Americans and a show of support for them."

It was a message repeated throughout the day by some 100 persons, many of whom arrived in Washington frustrated, bewildered and tearful.

The State Department paid for one member of each hostage's family to come to Washington. Many brought relatives, who paid their own way.

For some who came, the emotion welled so deeply inside that they could hardly speak. For others, the dozens of television cameras and microphones thrust out to them offered a welcome opportunity to express their sadness and, in many cases, their optimism, patriotism and faith in God.

"We came to glean a ray of hope," said Mary Jane Engquist of Burke, Va. Her sister, Kathryn Koob, is one of two women still held hostage. Koob, an employe of the International Communication Agency, was director of the Iran American Center, which helped Iranian students find colleges to attend in the United States.

"People are forgetting there are two women still in there," said Engquist, a staff assistant at the National Academy of Sciences. She was accompanied by her parents, from Jesup, Iowa, and another sister, Micki Koob, from New York City.

"This has been a unity-type thing," Engquist said. "It's been a reassurance" that U.S. officials "are doing everything they can. We have to maintain the dignity of this country. We can't let ourselves be blackmailed. These are important questions of national diplomacy."

It was comforting, she added, for her family to know it is not alone. "All of us are one big family," she said of the hostages' relatives.

Micki Koob said the briefings, which included long question-and-answer sessions with top State Department officials, were an opportunity "for families to get anything off their chest. It's been terribly frustrating because there are no clear answers."

The Koob family has written to Kathryn daily, but has had no word about her condition.

Carter's five-minute speech to the families "was very warm," Koob said. "He expressed great concern, and said he felt as if every person there were a member of his own family."

After the talk and a short question-and-answer period, Carter spoke to each family individually. He hugged and kissed and posed for pictures.

"It meant a great deal," Koob said. "Everyone felt he's handled this very well, and they wanted to personally express their gratitude."

For some, the trip to Washington was a chance to try to do something on their own. The wife of one hostage volunteered to speak to the Iranian militants holding the hostages. She was taken to the Iran Working Group office, where she talked by telephone to the captors, asking for news of her husband.

Judy Ehlenbeck, a secretary from Overland City, Mo., went straight to the Iranian Embassy on Massachusetts Avenue yesterday morning before the official briefing.She spoke to security guards about her brother, a Marine sergeant being held hostage, and was planning to return to try to talk to Iranian diplomats.

"I feel good," she said after the morning briefing. "We're sharing each other's experiences. It's very informative."

The meetings were very emotional at times, participants said. One family was concerned that their son not be branded a traitor for having issued a statement sympathetic to Iran.

The State Department tried hard to isolate the families from about 100 reporters who gathered outside the building. Several family members have complained of harassment by reporters during their ordeal. One family reported that members of a news organization entered their home while they were away and interviewed their young children.

The competition that the hostage story has sparked was evident yesterday as a crowd of reporters from St. Louis followed Ehlenbeck's family.

Gary Rebstock, with KTVI, said his station had selected Ehlenbeck's parents, Virgil and Tony Sickmann of Krakow, Mo., flown them 60 miles by helicopter to St. Louis and paid their way to Washington -- all in hopes of an exclusive story.

Ehlenbeck had promised an exclusive to the St. Louis Globe-Democrat, which paid her way here, but by the end of the day she was giving interviews to three networks and dozens of reporters.