When President Reagan addressed a National Space Club lunch last March he noted that sound doesn't travel in space, adding, "I'm not really going to believe that until I see Sam Donaldson up there."

The president may get the proof. The high-spirited ABC News White House correspondent is among several hundred U.S. journalists applying to fly aboard the space shuttle next autumn. Applications must be postmarked no later than midnight tonight.

"Often when I do things, people say I'm just grandstanding," Donaldson said yesterday. "That's not the case here. I made a very, very serious pitch." Among other things, Donaldson wrote in his application that he would do hard reporting on the trip. "None of us would go along as a cheerleader," he said.

Walter Cronkite, the grand old man of CBS television, who has covered the space program since it began, has applied.

"From a pure standpoint of personal satisfaction, the opportunity to see this globe of ours from near orbital space would be, you know, a satisfaction that could hardly be matched," Cronkite said yesterday. And journalists are needed in space, he added, because unlike astronauts, "We reporters are trained to observe and interpret for the average man."

Cronkite said that although he is 69 and unsure he could pass a NASA physical, "There ought to be a great advantage to prove that any old fart can do it."

The journalist selected is expected both to broadcast and write about the experience; applicants are required to write essays on how they will communicate from space and on the future of journalism in space. Some have written fervently:

"To beat through the air and clouds and sail through the vast, black ocean of vacuum; what must that be like?" wrote free-lance filmmaker and former ABC News correspondent Geraldo Rivera in an essay. "What joy must that experience hold for me and millions like me who have dreamed since Flash Gordon and Captain Video of one day shedding gravity's drag. What pride would a correspondent feel to file his report floating at earth's end and heaven's beginning."

Filling out the 12-page application forms has proven a challenge for many. "The thing that's amazing is I have a daughter who's applying to college this year and the similarities" in the applications are striking, said NBC News science correspondent Robert Bazell.

An NBC spokesman said that "NBC Nightly News" anchor Tom Brokaw will apply, but Brokaw couldn't be reached for comment yesterday. A source said that "CBS Evening News" anchor Dan Rather planned to apply, but a network spokesman said, "This will take the anchorman out of circulation for a long time, so this could have a bearing on who applies." At ABC, a spokesman said at least nine correspondents were applying. Asked if "World News Tonight" anchor Peter Jennings would apply, the spokesman said, "I don't think so."

NASA officials refused to release names of applicants, but a source said journalist Tom Wolfe, author of "The Right Stuff," planned to apply. Wolfe couldn't be reached. Other print journalists, including Art Buchwald, Hunter Thompson and Mike Royko, have written columns saying they wouldn't seek a shuttle berth.

One of the ABC News applicants, national correspondent Lynn Sherr, who has covered the space program for years, said, "Sports reporters get to go into the locker room . . . I want to do my job. I want to be able to explain what's going on out there."

Cronkite's application had led some applicants to wonder if there's really any point in going up against him.

"I think that I and a lot of other people would be damned insulted if he got it," said a television correspondent and applicant who asked not to be identified. "It's not that he doesn't deserve to go. As a child I watched Cronkite cover the space program. But if NASA wants Cronkite to go up, they shouldn't waste all our time."

NASA officials insist that everyone has an equal shot. "Sure, we could have picked a single individual," said Alan Ladwig, manager of NASA's Space Flight Participant program. "We considered that, but we decided to make it available to all those who meet the requirements."

The requirements include American citizenship, good health and a track record as a working journalist. There is no age limitation.

The selection process for the Journalist-in-Space Project, as it is called, is being run by the Association of Schools of Journalism and Mass Communication. Jack Bass, a spokesman for the project, said that 200 applications had been received by noon yesterday and hundreds more were expected. There have been applications from broadcast journalists and newspaper and magazine reporters.

Eight candidates will be chosen by each of five regional panels of academic and journalistic judges -- a total of 40. Then five finalists will be chosen by a national selection committee. On April 17, the winner and a backup chosen by NASA officials will be announced.

Sending a professional journalist into orbit may pose special problems for space officials. The journalist will be subject to a background check and must agree to ground rules to protect national security.

There are serious First Amendment questions involved, according to Mark E. Brender, an ABC News assignment editor who chairs the Media in Space Committee of the Radio-Television News Directors Association.

"People are taking it lightheartedly, but it's going to set tremendous precedents for the role of journalism in the future," Brender said. "Where there is very little law, precedence is everything, and if that first journalist is restricted in any way on reporting what he or she sees, there are real constitutional issues involved."

Brender added: "As far as I'm concerned, when that first journalist goes, the First Amendment goes with him."

Sherr of ABC said, "I find it hard to believe that one would be prevented from filing a legitimate story if there was a crisis" on the shuttle.

"The general feeling is they're going to have all the freedom they need," said NASA's Ladwig.

But what if the captain tries to stop a journalist from reporting some incident?

"That would get into censorship then," said Ladwig. "The journalist, as all crew members, is subject to the authority of the mission commander, but that doesn't mean the mission commander is going to be reading over the guy's shoulder and saying, 'You can't say that.' "

But what if such a situation arises anyway?

"Well," said Ladwig, "we'll just deploy him (into space) in that case." He quickly added that he was joking.