"I would like to have gone, but I guess they had to have someone to mind the store," says Kathy Ahern, the third floor receptionist at the new Reagan for President national headquarters in Arlington. Left behind to mind the store were five staff members, while most of the 200 to 300 workers who will fill the headquarters are in Detroit.

Hers wasn't the only undermanned office yesterday.

"No, she's not here. She's in Detroit," Robin Stein barks into United Press International's buzzing, flashing switchboard. "I can take a message. pYeah, the area code out there is 313. . . .

"Everybody wants someone who's out in Detroit," says Stein, coming up from behind the phone for air. Normally a news clerk in the UPI Washington bureau, Stein was filling in yesterday for the regular switchboard operator, who is routing calls in the wire service's Republican Convention bureau in Detroit.

A good chunk of the Washington-based press corps -- and a total of some 15,000 media personnel from around the country -- has transplanted itself to Detroit for the week, with news bureaus and press services falling into the hands of deputies and assistants. And among professional Republicans, the heavy hitters have gone off into the prime time of the convention, leaving offices manned largely by clerks with time to tune in the soap operas.

The UPI office, where Stein was pinch-hitting at the switchboard, was typical of the news bureaus that lost not only reporters and editors but office personnel in the migration to Detroit.

"She went because they wanted people out there who know what's going on," says Stein of the regular operator, adding somewhat defiantly, "That's why I was surprised they didn't take me."

Back six weeks ago it looked like Stein and editor Ted Shields would be traveling to Detroit after their names were posted on a tentative list. But when it became apparent that the nomination would be less than a cliffhanger, UPI decided to cut back. Sheilds and Stein were bumped.

"I suppose I was disappointed in a minor sort of way," says Shields, "but I'm not banging my head against the wall."

The Monday night cocktail hour crowd at the National Press Club bar had been depleted of nearly 65 percent of the regulars, according to Nour Hzyan of NEWS Photos-News Worldwide.

"As for me, I've covered too many of those things," says Hzyan. "If I can hide from one of them I'm very happy. Once is enough."

She says the journalists remaining to haunt the National Press Building are generally those who cover science, business or other nonpolitical beats and are just as glad to be left behind. "Many of the regulars really weren't looking forward to it. Besides, it's Detroit. I'm sure if it was in Hawaii there would be a higher percentage wanting to go."

Meanwhile, at the Class Reunion some three blocks from the White House, the traditional journalists' end of the bar was severely understocked. "I really miss the press people," laments Joan Grbach, manager of the establishment, whose clientele includes the elite among national political reporters. "But they've been gone on and off since the campaign began, so it's not really too different now that the convention is on."

Yet to escape similar boredom next month when the Democrats parley, Grbach plans to go to New York or a reunion with her press customers. One regular reported seeing 40 of Grbach's regular customers at Toots Shor's bar in New York during the last Democratic Convention. "I'm not going to miss the fun this time," vows Grbach.

On the Hill yesterday, eight reporters were parked in the Senate Press Gallery leafing through newspapers and digging deep for any scraps that might make a Sunday feature story. Usually up to 200 reporters file through the gallery in a day and the phones ring "hundreds of hundreds of times," according to the gallery's assistant supervisor, Bob Peterson. Yesterday, there were a mere "20 to 30 calls."

UPI sent 20 of its 63-person Washington bureau, and the Associated Press Washington bureau has dispatched 35 news staffers and 18 photographers. pIn addition, the wire services have deployed regional reporters from their state bureaus to keep tabs on individual delegations. Thirty-five Washington Post staffers have also made the trip.

The ranks of Republicans in town have also eroded to skeletal levels. Hardest hit was the Republican National Committee, which sent 200 of its 250 staffers to the convention. much to be in charge of." This week the staff is made up primarily of "functionaries" who are opening mail and attending to the all-important duty of keeping track of the solicitations.

Bulow says a television screen was brought into the conference room for viewing the convention. But yesterday, she says, the staff was catching up on soap operas.

Bulow herself took her 4-year-old son on a 2 1/2-hour lunch break during which they inspected the trains at the Smithsonian.

Bulow confirmed her office's laidback attitude: "We're taking it easy this week."