Diane Johnson, a mother of two from Dublin, Ga., was among the women whose husbands went to revolutionary Iran months ago in the service of their country. And she was among the women who gathered on the White House lawn yesterday for the nation's joyful reunion with the hostages.

But for Diane Johnson, there was no reunion.

Her husband, Marine Staff Sgt. Dewey L. Johnson, was one of the eight men who died in the Iranian desert last April in the burning ruins of "Operation Blue Light," the unsuccessful attempt to rescue the American Hostages in Tehran.

At the invitation of President Reagan, she came to Washington for an emotional meeting yesterday with the 53 people her husband had hoped to rescue. e

"I don't know, I really thought I ought to be here," she said quietly yesterday afternoon. Her husband, she said, had carried out his duty, and now she felt that she, too, "had a duty" to be present for the hostages' official welcome home.

Thelma Bakke, the mother of Air Force Capt. Richard L. Bakke, another desert casualty, expressed the same bittersweet sense of melancholy in a brief conversation with the president yesterday. "I'm glad we could be here," she said, "but I'm finding it hard to take. You're happy and you're sad."

Family members of all eight men who perished in the rescue effort attended the White House ceremonies, standing together at the front of the audience with Col. Charles Beckwith, the Army veteran who led the aborted commando raid. Afterward, the eight families had a brief, quiet meeting with President and Mrs. Reagan and then received the thanks of the returned hostages.

They waited silently in the White House Green Room while the Reagans greeted the returned hostages in the adjoining Blue Room. Eventually, the president and First Lady entered the Green Room. At first, according to a White House official who was present, there was silence on both sides.

Then one woman stepped up to the president and said, "I just have to hug you." That broke the ice, the White House aide said, and all the families came over to accept the president's thanks.

Reagan then led the group to the reception in the Blue Room, where military chaplains took the families around and introduced them to the former hostages. "They all said they were very, very thankful," Diane Johnson said later.

That gratitude was evident earlier when L. Bruce Laingen, the ranking diplomat among the former captives, opened their morning news conference at the U.S. Military Academy at West Point, N.Y., with an expression of thanks for the rescue attempt.

"At this first opportunity this morning," Laingen said, "back on American soil, we want to reach out with affection and undying respect to the families of the eight men who did not come back. Their readiness, as well as that of all the others on that mission, to put their lives on the line because they wanted us to be free will always be a symbol of the best in American dedication to principles of freedom that we all enjoy."

At the afternoon ceremony on the White House South Lawn, Reagan noted that those present included the families of "the eight heroic men who gave their lives in the attempt to effect your rescue.

"Greater glory hath no man than that he lay down his life for another," Reagan went on, paraphrasing the words of Christ in the gospel according to ST. John.

The eight servicemen died April 25 in the predawn darkness near the Iranian desert town of Tabas.

They were part of an elite 90-man force that had volunteered for a daring helicopter raid across the length of Iran to snatch the American hostages from their makeshift prison at the U.S.Embassy in Tehran. The raid was called off at a midway rendezvous after three of the eight helicopters experienced mechanical failures. As the helicopters and six C130 transport planes were preparing to return to waiting aircraft carriers, one helicopter collided with a transport loaded with fuel. The eight men died in the resulting explosion.

They were Air Force Capt. Richard L. Bakke of Long Beach, Calif.; Marine Sgt. John Davis Harvey of Roanoke, Va.; Marine Cpl. George N. Holmes Jr. of Pine Bluff, Ark.; Marine Staff (SECTION) gt. Dewey L. Johnson of Dublin, Ga.; Air Force Capt. Harold L. Lewis of Mansfield, Conn.; Air Force Tech. Sgt. Joel C. Mayo of Bonifay, Fla.; Air Force Capt. Lynn Davis McIntosh of Valdosta, Ga., and Air Force Capt. Charles T. McMillan II of Corryton, Tenn. g