This is the climate that tries the soul, when the faint of heart retire to shore and mountain and the August streets and corridors of the nation's capital wilt in steamy near-emptiness. But some summer soldiers labor on. Today's dispatch from the front:

The corcoran Gallery of Art is housed in one of Washington's few public buildings with no air conditioning and yesterday the stultifying atmosphere from a stalled Bermuda high had the place almost to itself.

A few stole art lovers stood facing walls here and there, little islands of moist flesh, dressed for the season: more casual than Healy's "Abraham Lincoln" in his black coat and bow tie, but more discreet than the "Reclining Nude on Green Couch" by Pearlstein. She was the only one who seemed really comfortable.

The huge skylights of the century-old Corcoran, which bathe its art in a natural sun glow, also help send tempertures in some of the rooms soaring as high as 90 to 100 degrees.

It was so hot yesterday the young woman in "Mercy's Dream" had swooned and loosened her blouse. Andy Warhol's "Mao Tse Tung" was being cooled by a floor fan.

All were dwarfed by the massive columns and broad marble staircases in the huge old building a block from the White House.

"Just look at 'Niagara Falls' and imagine the water temperature. Probably 45 degrees. Imagine you're in it up to your knees," suggested visitor David Neumeyer, as he admired the large masterpiece by Frederic E. Church that was cascading vast, foaming masses of finely detailed water.

Neumeyer had come here from much cooler Providence, R.I., where he lives. "I could spend weeks here despite the humidity," he said. "Washington is the best place I know for museums."

However, as people usually do, he had other reasons for coming during August. Under a government grant, the Reginald Heber Smith Fellowship, he will attend training sessions at Howard University next week. The program is designed, he said, "to attract young lawyers into proverty law.

And after that? He grinned: "I'm off to the Berkshires, Natucket and Maine."

Officials of other museum load up with "humidistadts," "hydrothermographs," "psychrometers" and other specially engineered climate control and monitoring devices in order to prevent their art from, as one put it, "shrinking, swelling, dripping, flaking, cracking or otherwise self-destructing" in weather like yesterday's.

To avooid such trageties, museums can obtain exemptions from Peeseident Carter's energy-saving 78-degree thermostat rule.

The National Portrait Gallery, for instance, has teams of engineers monitoring its temperature and humidity around the clock to protect the 4,500 art objects there.

"It's so nice in here, I don't go out to lunch. It's even better than home, because it's less humid," said Suzanne Jenkins, the Portrait Gallery's registrar.

The White House has raised is thermostat settings to 78 degrees even though it houses several hundred valuable works of art. At least one person whose art is on loan there has complained that this tropical shift could damage the objects, according to Betty Monkman, the White House registrar.

But so far, she said, there's been no sign of a crackup.

Art objects can adapt to almost any given climate, the experts agreed. It's sudden change that drives them off the walls.

In any case, for the Corcoran Gallery, the solution is a matter of something between $400,000 and $1 million, according to the Corcoran's Sheila Mc.C. Muccio, whose duties include raising money. "That's a ball park figure for the coast of instslling climate controls' here," she said.

The museum staff offices, which also house rare old books, are air-conditioned. So are some storage areas and one top-level exhibit room, that contains such abstract treasures as one 20 or 40-foot-long canvas filled with varicolored vertical stripes.

"All we need in Washington is another mile of elevation," said Muccio, a Foreign Service wife who has lived in many hot places, including Guatemala. None, she said, was worse than this.

"Britain used to list Washington as an unhealthy' post," she added.

Some paintings of apparently British temperament are removed annually from the Corcoran's walls to the climate-controlled storerooms during weather traumas. But most of the collection remains where it is, Muccio said.

"After all. the great strength of this museum in its 19th century collection. These were done in a time when there was no air conditioning You could say they grew up without it.' They've never been in air conditioning."

Art in this case was not imitating life. The 'Niagara Falls' remained cool and alluring before a sweating quartet of German tourists. They were drawn to it like magnets.