Seven a.m. on what already feels like another 90-degree scorcher. Three laborers check in for the day's work at the Montgomery County building site. The boss notes their arrival:

Richard.

Larry.

And Dr. Schulman.

An unusual roster for unskilled muscles, no doubt about it, acknowledges project foreman Bruce Oranburg, whose firm is building 24 large houses in Cabin John.

But Chevy Chase psychologist Steve Schulman -- dressed for the job in thick boots, shorts and T-shirt -- is a full-fledged, signed-on member of the crew: at least on Wednesdays.

Once a week this summer, Schulman a husky 35, trades his comfortably airconditioned desk job for 8 hours of hard, dirty physical labor under a sometimes brutal sun. And he exchanges his standard professional consulting fee for a laborer's 4 bucks an hour.

"My gross" for the day, he says, "is $32." But after deductions, the Friday paycheck reads "$29.87."

What is he trying to prove?

For one thing, one of the 4-bedroom, 3-bath homes going up is his.

For another (and to his surprise), "I'm having a great time.

"I work hard, but I don't have to think hard. There's no ambiguity to it. Even if I just dig a ditch or clean up a mess, I've done something I can see. In my own work I'm never done. Things are never that clear."

He looks on the summer job as he does mountain backpacking, another often-strenuous pastime. "To walk, to expend energy, I realized that appeals to me."

The 7 a.m.-to-3 p.m. shift is physically exhausting, he says, but also refreshing, keeping him "very alert" when he sees private patients later in the day.

Obviously, if he had to put in a 40-hour week, 50 weeks a year, his view might be less enthusiastic. Though one fellow crew member remarked to him: "It sure beats sitting behind a desk, doesn't it?"

Schulman's first idea was that he and his wife, also a psychologist, would take the summer off and join a small crew building their own architect-designed home. But that turned out to be "impractical." When they decided, instead, to buy a home planned for Universal Construction Company's Evergreen development, Schulman asked Oranburg to hire him as a laborer.

"It was sort of an impulse. Nobody had ever asked him before," says Schulman, "but he thought it was a great idea."

Adds Oranburg, who at 27 has worked at construction sites for half his life: "I like somebody trying to be a part of his house, somebody learning about the variables that go into a home. There's so much to it, and a lot of people take it for granted."

There also was a practical consideration: At the pay scale, "It's very difficult to get good laborers," says Oranburg. "It's not an easy job, and it's not a fun job, but laborers are a very important part of the work."

"I'd never done any construction work before, says Schulman, whose tan rivals that of his Wednesday co-workers, but he remembers "when I was a kid, construction sites fascinated me."

His inexperience was no barrier, since the job doesn't require any. Mostly he hauls, digs and cleans up leftover debris. Union rules prohibit him from carpentry or other skilled work.

Early on he "stomped down on a nail," requiring a trip to Sibley Hospital.

He switched to a heavier pair of boots.

Schulman works frequently on his own house, but much of his time is spent at other homes in the project, some of them much further along than his. That has enabled him to make changes he and his wife might not otherwise have considered.

As a result of what he saw on nearly finished models, he says, "We doubled the size of the pantry and we moved the windows in the bedroom farther apart so the bed would fit between them."

One of his tasks was to dig the water-runoff system for his house before the concrete was laid, which gives him a certain advantage. "I would never have known what was under my house."

All of this has boosted Schulman's confidence about future projects around the house. "It would not intimidate me now to finish a basement or build a deck. I just watch everything."

As far as Schulman can tell, he gets along well with the rest of the crew, often sharing his half-hour lunch break with fellow laborers, one of whom is between semesters at college. Is there any resentment?

"I haven't felt that. I was afraid of it -- of their thinking I wasn't taking seriously what they do. But that hasn't been the case. They probably think it's a little bit crazy."

With Schulman on site, it's natural to think that his co-workers and the construction company might be giving his house -- due to be completed at the end of August -- special attention. But he doesn't think so. With a loyalty any boss would welcome, he thinks the firm is doing "an equally good job" on all the project's houses.

Foreman Oranburg believes many construction firms would be hesitant to hire a buyer like Schulman to help build their own home. Although reluctant to consider taking on anyone else, he doesn't rule it out. "It depends on who it is."

Meanwhile, Schulman spots another dirty chore in his uncompleted basement. Overnight rains have washed a layer of mud from the hillside over the concrete floor. He may be paying tens of thousands of dollars for the place, but at $4 an hour it's his job to clean it up.