The air comes in and hangs around, hot and sticky and stubborn. The populace sweats and tourists swelter. Temperatures hit 90-plus for days on end with no relief in sight. There is a run on air conditioners and fans. The iceman goeth.

But the weather experts aren't impressed.

"I don't think it's any big deal," says Dr. Robert Livezey, hard-hearted research coordinator at the National Weather Service's Climate Analysis Center. "Certainly it's hot and humid and muggy, but it often is in the second half of July."

As the Washington region braces for its 10th straight day of steamy temperatures in the 90s, the folks who know about such things said yesterday that our local heat wave is not, repeat not, a record. And meteorologist Ross LaPorte is only half kidding when he pores over all the highs and lows and concludes:

"It's not the hottest summer on record--it's the hottest summer this year."

The summer of '80 was much worse, a real "horror," he and his colleagues at the Weather Service remind current sufferers. That's when temperatures topped 90 degrees for 21 days in a row. Of course, they add, that was in August of 1980, and we haven't reached August yet this year.

"If this is anything, it may be the start of a heat wave," said Robert Churchill, a meteorologist technician. "Sometimes you have to wait until it's over" to see if any records have been set.

There was some relief from the heat for most local residents last night, as a line of thunderstorms moved through the area and dropped temperatures sharply, if temporarily. But the same storms brought a different kind of discomfort to thousands of others, as high winds and heavy rains caused scores of power outages, chiefly in Northern Virginia.

Daily high temperatures here since July 12 have ranged from 90 degrees on July 14 to a peak of 99 degrees on July 17. The normal for this time of year is 88. Yesterday the mercury climbed to 95, and the humidity averaged about 70 percent.

That's hot enough for Cis LoBianco, an office manager at AC Services, an air-conditioner company in College Park. "We're getting 50 calls a day from people who want to rent window units and other types of air conditioners," she said yesterday. "The phone starts ringing at 6 a.m. and doesn't stop until 11 p.m."

The heat wave is setting records at Virginia Electric & Power Co. and at Potomac Electric Power Co. Vepco and Pepco both met a record demand for electricity Monday, providing their customers with 8,930 megawatts and 4,283 megawatts, respectively.

There also has been a run on ice at liquor stores, gas stations and convenience markets. A 7-Eleven food stores spokesman says its 561 area stores used 376,000 eight-pound bags of ice in June, and July is sure to top that.

But about the only history-making weather statistic offered up comes from meteorologist Dave Caldwell, who reports that a record was set Saturday when the area had the highest minimum temperature--84 degrees--ever recorded here since people started collecting such data 111 years ago. The highest recorded low temperature previously was 82, set on July 9, 1981.

The weather outlook through the weekend is for temperatures in the mid-80s to 90, forecaster said.

Last night's thunderstorms, which began about 7:30, helped drop temperatures into the 70s but also left about 39,000 area residents without electricity for varying periods of time. Northern Virginia was hardest hit by the storms, which dumped more than an inch of rain in some sections in about 30 minutes.

A Vepco spokeswoman said the 29,000 outages in its service area were widely scattered. Pepco reported about 9,000 customers without power in Maryland at the height of the storm. The companies said trees on electrical lines were the main problem.

National Weather Service forecaster Harold Hess said there were reports from Arlington and Montgomery counties of winds gusting at 50 to 60 miles per hour, and hail of nearly an inch in diameter was reported in Damascus in upper Montgomery County, he said.

A sharp gust of wind was blamed for the collapse of two large window panels at an Arlington supermarket in which 12 shoppers were slightly injured by shards of glass. The incident occurred shortly after 8 p.m. at Shoppers Food Warehouse, 6255 Little River Turnpike. None of the injured required hospitalization, police said.

In other incidents, officials at Jefferson Memorial Hospital in Alexandria said they were trying to identify patients who could be sent home early after rain started pouring in through a hole in the roof, and television station WETA (Channel 26) was off the air for more than three hours after its transmitter was knocked out by the storm.

"We . . . can't get the cool front," a weather service spokesman said. "That's why we're getting the thunderstorms." He did, however, offer the cautious prediction that there might be some relief starting Monday.

Unfortunately, the spokesman said, the weather all over the country is pretty lousy. But the forecasters are still pulling for us. "We're human, we suffer, too," said Churchill. "And when it's hot like this, our workload increases because of all the questions we get about the weather--and not only at work."