When Marine Sgt. John D. Harvey brought his wife and baby daughter home to Roanoke, Va., for Easter weekend, he told his parents he was training for a "secret mission."

John and Jean Harvey had no idea what that mission was or even that their 21-year-old son was outside of the country until 9:30 a.m. yesterday, when two Marine officers knocked on their front door and said their son was "missing and presumed dead."

The Defense Department said yesterday that Harvey, an expert in helicopter electrical systems stationed near Camp Lejeune, N.C., was one of eight servicemen killed in the aborted attempt to rescue the American hostages in Iran.

According to the Harveys and others, the silence Sgt. Harvey had maintained for nearly six months was kept by the seven other men who perished when a C130 transport plane and a helicopter collided in the desert southeast of Tehran.

Relatives said yesterday the men had maintained strict secrecy about their mission, refusing to explain where they were going or what their mission was.

"He didn't give us any details of it," said George Holmes Sr. of Pine Bluff, Ark., whose son, Marine Cpl. George N. Holmes Jr., 22, was one of the dead.

"He hadn't even told us he had left the country," Holmes said. "He sent his stuff home, even his last paycheck, clothes and stuff; mailed them home and said he wouldn't be needing them for a while."

Joe Holmes, an uncle of the deceased Marine, said the family knew "he had been training out in Arizona under conditions similar to Iran's for about a couple to three months.

"It was pretty secret, but we knew something was up. Sometimes George would just up and leave, and we wouldn't hear from him for a while," Holmes said.

In addition to Harvey and Holmes, and Defense Department listed the dead as: Marine Staff Sgt. Dewey L. Johnson, 31, of Jacksonville, N.C.; Air Force Capt. Richard L. Bakke, 33, of Long Beach, Calif.; Air Force Capt. Lynn D. McIntosh, 33, of Valdosta, Ga.; Air Force T/Sgt. Joel C. Mayo, 34, of Bonifay, Fla.; Air Force Capt. Charles T. McMillan II of Corryton, Tenn., and Air Force Capt. Hal Lewis, of Willimantic, Conn.

Two Air Force men and two Marines suffered burns in the nighttime collision, the Defense Department said. The injured were Marine Majs. Leslie B. Petty, 34, of Jacksonville, N.C. and James H. Schaefer Jr., 36, of Los Angeles.; Air Force 1st Lt. Jeffrey B. Harrison, 26, of Warren, Ohio, and Air Force Staff Sgt. Joseph J. Beyers III, 37, of Charleston, S.C.

Prior to their secret training for the rescue attempt, the Air Force men apparently had been stationed at Eglin Air Force Base near Pensacola, Fla. the Marines had been based at New River Marine Corps Air Station near Jacksonville, N.C.

Relatives of the dead said they were told yesterday that the government did not know when or if the bodies would be shipped home. Defense Secretary Harold Brown told a press conference that the United States was seeking return of the bodies through diplomatic channels.

Mary Mayo, mother of Joel Mayo, 34, the navigator of the C130 transport plane, said yesterday that her son had volunteered for the assignment.

"He asked for this mission. That's all I can tell you," said Mrs. Mayo, interviewed by phone in Bonifay. "He went down for his country."

Asked if she believed the mission should have been launched, Mrs. Mayo said, "Yes, I do. We need to get our boys out, move our a-- and blow the whole works up . . ." After pausing for a moment, she added, "The 50 hostages are not worth thousands of us."

George Holmes also said he approved of the rescue attempt.

"I think if was fine. It was a risk worth taking. That's what I thought beforehand. I don't change it now," Holmes said.

The wife of Lynn McIntosh, the pilot of the C130, called a friend in Georgia sometime after midnight yesterday to say that she was worried about her husband.

Ann McIntosh, who had been watching television in her quarters at Eglin, told the friend she had just been frightened by a news bulletin. Mrs. McIntosh said she heard that a C130 had crashed in the failed rescue attempt in Iran.

"She didn't know where (her husband) was and that's why she was so scared," said another friend who spoke with her.

The young Air Force wife told friends that the only thing she knew was that her husband had been ordered away on a mission four or five days earlier. She said her husband never discussed his missions in the 8th Special Operations Squadron.

It was several hours later, according to friends, that Ann McIntosh was told her husband was among the eight dead men left on the salt desert in Iran. t

Relatives of the casualties said yesterday that the servicemen had not contacted their wives or parents for four or five days before yesterday's attempted raid.

Those relatives who consented to telephone interviews yesterday said they were not angry at President Carter for the raid.

Many relatives, according to friends, were extremely upset early yesterday because of the lag between the first news reports of servicemen killed and official notification by the Defense Department that their husband or son was among the dead.

Family members said yesterday they were also confused and upset over the question of whether bodies would be returned to the United States.

Asked her feelings about any future diplomatic efforts to gain the return of the bodies, Mrs. Mayo said. "I'm hoping they will. Whatever's left, I want it brought back."