Washingtons returned to their parks, sidewalks and back yards yesterday as cleaning winds blew in from the west, ending almost three weeks of scorching pollution-filled heat in the area.

Forecasters called for continued fair weather through the weekend and possibly until Wednesday , except for a chance of thunderstorm Tuesday. High temperatures should range from the mid-80s and lows from mid-60s to mid-70s.

Under bright, wind-spread skies, thousands of downtown employees emerged from their concerte officers yesterday and flocked once aginst to city parks that had been virtually deserted in recent days. People on lunch break munched sandwiches and celebrated the merciful return of decent weather.

"It's great being able to breathe again," said julie Gilbert, an Allegheny Airlines secretary sharing lunch with three companies in McPherson Square.

"You can see the city. You can see the buildings, It's unreal," said Paula Baker, a creative copying assistant with the J. Walter Thompson advertising firm.

She said regularly eats in the park but until yesterday had not been out in about two weeks.

During the heat, she said, "a lot of people would maybe go out to get a sandwich but them come right back in "to seek the comfort of their air conditioned officers.

National Weather Services statistics for yesterday confirmed what everybody knew: temperatures were down, humidity was down and pollution was down.

The temperature reached an official high at National Airport for this time of year and well below the 95-to-100-degree readings of recent days. It was also the first day the thermometer did not reach or exceed 20 degrees in the last 10 days.

Humidity dropped from a midday level to 60 to 65 per cent Thursday to 35 to 40 percent yesterday.

The air quality index also dropped substantially from a "very unhealty" reading of 115 Thursday to a "fair" level of 37 yesterday, according to the Metroplotan Washington Council of Governments. COG ccnceled its seven-day-long pollution alert at noon yesterday.

A cold that moved into the Washington area late Thursday pushed the hot, stagnent air eastward toward the atlantic, lowering temperatures from the mid-90s to mid-70s. Scatterres thundershowers also dumped at National Airport and brought some relief to dought stricken areas of rural Virginia and maryland.

The Potamac River, which has been flowing below normal levels most of this month, receiveing a slight increase from isolated showers in the upper reaches of the 14.000 square mile Potamac basin.

U.S. Geological Survey hydrologist Bernie Helinsky said the river at Washington was flowing at 1.7 billion gallons per day aat 3.30 p.m. yesterday, up from 1.5 billion gallons the day before.

Rain in accumulations in the upper basin Thursday rranged from 1.60 inches in Gardiners. Pa., and .60 inches at Cumberland and nothing at Frontt Royal.

The National Weather Service called for fair skies today and Sunday with highs ranging from 85 to 90 degreeres but with less humidity than in recent days. Overnight lows this weekend should range from 62 to 68 degrees.

Yesterday's light, brezy air lured thousands of downtown employees into Lafayette Park. Farragut Square and other grassy spots during the midday lunch break.

In McPherson Square, all appeared to be back to normal as three winos in laceless shoes and mission house hand-me-down clothes slumbered tranquilly under a hugh southern red oak.

Camero-toting tourists flocked in front of the White House, but Executive Protective Service police officers at the executive massion gates said there seemed to be no more than doing the excessive heat earlier this week.

The tourists flow "seems about normal," said officer G.E. Shovlin.

Likewise, said several street vendors hawking trinkets and food, tourists seem undaunted by the heat.

"My sales are actually down today," ice crean and novelty vendor Daniel J. Walsh at Pennysylavania Avenue and 15th Street NW. "I did splendidly yesterday" when it was 95 degrees.