IT'S CLOSE TO 5 last Thursday afternoon and the sloping grounds of the Merriweather Post Pavilion are almost deserted. In three hours, 14,000 fans will pretend they're sardines. Right now there are more wires than people, and the wires are strung out in a dozen directions: from center stage to sound crews out front and to the side; from stage to the mobile recording studio out back; and farther to a giant satellite dish that will broadcast that night's Men at Work concert to 80 radio stations across the country.

Men at Work have been at leisure at a nearby hotel, but their work night is about to begin with a sound check. A year ago, any member of this Australian quintet might have been content to chauffeur a limousine, but platinum-plus record sales now allow them to ride in the back seat. Their debut album spent 15 weeks at the top of the charts, the longest stay there by a new group since the Monkees in 1966. Looking bewildered and grateful rather than cocky and rich, the Men saunter to instruments pretuned by roadies and strike at chords that become decreasingly tentative. What is being sought here is not pitch, but level. Each new concert venue must be tested, like a balloon blown just short of popping. The stakes rise when the sound moves to the airwaves.

Road manager Dennis Dunstan sits alone in the middle of 5,000 seats, listening hard and shouting gutteral but obviously encouraging phrases to his working Men. After 35 minutes, with the songs having reached full concert power, the Men make like a whistle has blown and saunter back to limousines that rush them back to the hotel.

THE MEN who continue working are not rock stars and therefore not in capital letters. Their rewards are in weekly paychecks and 25-ounce cans of Foster's Lager, industrial-size containers cooling in buckets of ice that dot a temporary command center. These are the essential technicians of rock; like the offensive line in football, they are not noticed until something goes wrong, and tonight everybody's working hard to make sure nothing goes wrong.

That's because the concert is a string of firsts: the first live (although slightly delayed) satellite broadcast for the new ABC Rock Network, the first live radio concert from the Post Pavilion, Men at Work's first live broadcast. The hub of energy, mission control, is the big black Record Plant truck, a mobile 24-track recording studio that looks imposing enough for Darth Vader to drive it. Everyone who wanders in or out of it is wearing headphones to communicate past twin walls of concrete and sound. Even then, the music can't be heard over the engine and generator rumble coming from buses and trucks that engulf the backstage parking lot.

"There are waves of tension in an event like this," says Peter McIan, the group's producer, who has flown in from Los Angeles to do a live mix on the concert. "Before you get to the gig, you have to make sure you've done all your homework--what can go wrong, how to prevent it, developing as many backups as you can. Then you get to the gig and try and focus on what you're doing. In a peculiar way, that's relaxing compared to the preplanning. Then at the end of it, you wonder how it really turned out.

"I like doing it this way," McIan says. There's an element of being on the edge. You either get it or you don't, there's no chance to go back and sweeten it. And if something breaks in the truck, it's broke. There's not a lot you can do about it so you hope everything stays together in one piece. It's pretty much going to be as you hear it, a live mix."

Which is, of course, why McIan is there. He knows the group's sound inside out. His job is made easier, he says, by the fact that "what most Australian bands have in common is going into the studio and playing as live as they can. You're not stuck in a situation where you're performing and you can't really fulfill the audience's expectations."

ALL THE PLANNING hadn't figured on a little glitch in the satellite dish parked at the edge of the lot and pointed skyward; the malfunctioning part is quickly replaced. At 11 that night, the dish is supposed to bounce a stereo signal off the 15-foot wing of a Wetsar sattelite 23,508.9 miles above the earth (a computer readout tells the crew exactly how far the satellite is from that particular point on earth). The 50,000-mile trip, from Columbia to sky to receiving dishes around the country, will take half a second.

The dish has its own crew, with facts marshaled for maximum effect. "It only has 20 watts per channel," says Jeff Sudakoff, talking technical, "BUT . . . the antenna has 52 decibels of gain, which is the equivalent of multiplying that by 130,000, so by the time it comes off the antenna, the effective power is about a million and a half watts." No wonder you can't hear anything in space.

McIan heads into the Record Plant truck for some last-minute levels. Ty Ford, a Baltimore deejay who will share the night's hosting duties with Dave Thompson of WRQX-FM (Q-107), is looking over his script. He will tape some commentary to be cut in during the 45 minutes between the concert's end and the national broadcast. The delay was inspired partly by the Men's embarrassing experience during the telecast of this year's Grammy awards, where the sound was so bad people might have been excused for wondering why they'd just been named Best New Group. It's also a safety precaution, a change to control and define the sound.

"I'm also on standby in case something happens during the show--if a mike falls over or the lights fall down," says Ford. He and Thompson will also "warm up" the fans to get some crowd sounds on tape for "ambient purposes."

IN THE sound truck, McIan and Dave Hewitt, the Record Plant's chief engineer for remote recording, are working on schedules, setting up an airtight script: dead air on the airwaves is a sin, and the "ambient" sound of Men at Work fans cheering lustily will provide a perfect cover. The crew has to do a bit of editing to keep the broadcast at 90 minutes (it will go over by seven minutes), inserting the deejay patter and a handful of commercials (mostly from sponsor Atari).

In a small camper nearby, executives of ABC Radio are sitting on pins and needles, watching the concert on a single-camera television monitor, but mostly listening to a live feed from the Record Plant truck. It's sounding very good ("it's HOT!" one executive says) and everybody looks relieved as the night wears on. Denise Oliver, who was once program director at DC-101 and WIYY in Baltimore, is now president of the ABC Rock Network. Although the network has been in operation since December, "this is our christening, our first live rock concert," she says. Two months in the planning stages, the Men at Work concert is being beamed into 80 cities, including the top 13 markets. Audience estimates range as high as 5 million.

The dish will send out a stereo final-mix, "just like it comes out of your stereo," says Bill Battison, ABC's vice president of planning, finance administration and satellite development. "It's as close to a live concert as you can get. There's nothing like live radio."

Inside the wood- and baffle-paneled Record Plant truck, Dave Hewitt is deferring to McIan and his assistant. He's acting more the traffic cop, the train conductor, keeping things flowing smoothly and on time. His crew is busy cross-fading sounds, cuing up different reels, making sure all the spots get in.

"Three seconds, then we're out of the commercial into the next song," someone says softly. The playback fills the truck, sounding brisk and clean (the concert has also been recorded and stored on a 24-track machine). Spirits are loose despite the deadline tensions. Big reels of two-inch tape are whipped on and off the tape decks as the crew juggles the playbacks into a seamless jigsaw puzzle of sound. It all comes out perfectly, and halfway through the broadcast, someone calls the ABC suite at the hotel. "Colin lead singer Colin Hay answered the phone and seems to be enjoying the broadcast," someone says, adding with a laugh, "though I don't think they're into nuances at this time."

At the hotel, the ABC suite resembles a post-election victory party, with a lot of back-patting and hand-shaking punctuating the frequent fill-ups from the bar. Hay and the rest of the band have listened to the delayed broadcast long enough to know they have been well served, and they slip into a subdued party attitude before slipping away to well-deserved rest.

After the broadcast, Dave Hewitt admits, "I think we're in pretty good shape. We did have a small problem with one of the two-track machines that bailed out. It was a rental machine and that always happens when you're not maintaining your own bits and pieces. It forced us to do a little chicanery but it worked out."

By 4 in the morning, the backstage parking lot is empty. The show is over.