CAPE CANAVERAL, Fla. (AP) _ Journalists are flocking here at record rates to cover the launch of the first U.S. manned spaceflight since the Challenger disaster shook certainty about the space program's safety.

At least 5,000 journalists had asked for credentials by Tuesday to cover the Discovery mission, scheduled for liftoff Thursday morning.

''Everybody thought shuttle flights were routine. Challenger proved it's a risky business,'' said Robert Hotz, former editor of Aviation Week & Space Technology magazine and a member of the presidential commission that investigated the Challenger explosion 32 months ago.

All four national television networks will cover the launch live this time. Only CNN had live coverage when the Challenger exploded 73 seconds after liftoff, claiming the seven astronauts' lives.

Jerry Hannifin, a Time magazine correspondent who has covered every manned space mission, recalled one colleague's decision several years ago to stop covering launches routinely. ''To his embarrassment now, he said the shuttle was just like a 747 taking off.

''But we're not sitting here on a body watch,'' Hannifin said. ''The U.S. return to manned spaceflight is the biggest story of this decade and it's our mission to inform our readers.''

''It's frightening because we don't know if everything will be OK,'' said Judith Weiner, reporter for France-Soir newspaper. ''But it is also exhilarating.''

She was among the large foreign press contingent, including representatives from China, Australia, New Zealand, Brazil, Iceland, Italy and more than a dozen other nations that have been accredited. Two Soviet journalists asked for credentials, then canceled.

''Public interest in the space program has continued to grow,'' said Dick Young, NASA spokesman at the busy press center.

''There's a zoo out there,'' he added.

Young and other NASA officials were also dealing with news representatives upset about unprecedented plans to restrict the number of journalists covering the launch at the press center, about four miles from the launchpad. The restrictions follow Air Force recommendations that cited safety concerns.

Discovery accreditation requests are the most ever received for a space mission. Young said in the past, about 70 percent of those accredited have shown up.

The previous record for journalists was 2,700 at the first shuttle launch and about the same number at the Apollo 11 and Apollo 17 moon missions. There were 1,467 for Challenger.

''This is a significant piece of American history,'' said Mark Kramer, a CBS News special events producer coordinating the network's 100-person operation here. ''This is not a packaged story like the national conventions, where the outcome is known.''

CBS coverage will include Wednesday and Thursday ''Evening News'' broadcasts from the cape with anchor Dan Rather and live coverage of the launch.

ABC, with anchor Peter Jennings, and NBC, with Tom Brokaw, also will carry live coverage of the launch and anchor their news shows from the space center. CNN will have anchor Bernard Shaw leading its live coverage.

The networks were working out of new, larger buildings constructed since the Challenger launch.

Young said the National Aeronautics and Space Administration accredits virtually anyone who is a legitimate journalist. College journalists are accredited, although the space administration draws the line at high school reporters.

Only 1,800 of the journalists will be permitted at the press center, and NASA has set up a second press area 7.5 miles from the launchpad for the remainder.

The restrictions resulted from an Air Force study spurred by the Challenger accident and the subsequent explosion of a Titan rocket launched from Kennedy Space Center. The study calls the press center hazardous because of the possibility of debris from an explosion falling near the launch site.

Young said the 1,800 figure would permit all news media under deadline pressure adequate coverage. But some veteran space reporters were angered by the restriction. Rep. Bill Nelson, D-Fla., who flew on a shuttle mission, also protested.

''We do not feel NASA is in the position to tell us how many people we need to cover a story. On principle, we will never buy that,'' said Edward H. Kolcum, a senior editor for Aviation Week.