The great dirty balloon of heat and humidity that hung over the Washington area for the last week finally drifted out to sea yesterday, nudged by kindly winds from the northwest bringing fresh air and somewhat lower temperatures.

But the relief may be short-lived. National Weather Service forecasters say more humid, muggy weather with temperatures in the mid-90-degree range may return tomorrow and continue through Saturday.

The one bleak consolation is that the weathermen don't expect the scorching 100-degree heat of last weekend. On Sunday, the thermometer reached 100 degrees, a record for the day. The low temperature that morning was a steamy 81 degrees, tying the record "highest low" temperature ever recorded here on June 30, 1959, and July 27, 1930.

At noon yesterday, the Metropolitan Washington Council of Governments lifted its six-day-long air pollution alert, as the air quality index fell to a "fair" level of 38. It was back up to an officially "unhealthy" 65 by 3 p.m., COG said, but was not expected to return to the alert stage of 100 today.

The highest level reached during the pollution alert, which began last Tuesday, was 110.

The alert period coincided with seven consecutive days of stagnant air and temperatures in the 90-to-100 degree range here.

Weather Service forecaster Charlie Archamblaut said yesterday a cold front moving in a southeasterly direction came through the Washington area at about 3 a.m. yesterday, breaking the heat spell. "It also brought in lower level winds to help push out some of the pollution," he said. yesterday's high temperature was an even 90 degrees, slightly above normal for this time of year.

The front is now stretched from about Cape Hatteras to southern Illinois, but "may be shoved back this way" sometime tomorrow, bringing warmer, more humid air, Archamblaut said.

Temperatures are expected to stay down in the mid-80s today, however, with a 50 percent chance of thundershowers.

Last week's heat spell was one of the worst here in recent years, especially because of the high nighttime temperatures. But National Weather Service records dating back to 1870 show many similar periods of intense heat and some that were far worse.

In July 1930 the city was hit with four consecutive days of blistering 100-degree heat with the temperature soaring to an all-time record high of 106 degrees on July 19.

The day before, when the thermometer hit 102 degrees, a 57-year-old manager of a Connecticut Avenue apartment building died of heat prostration, according to a Washington Post report.

"Thousands Sleep in Park," said a headline in July 21 editions of The Post after the temperature hit 103 on July 20, and residents fled their un-air-conditioned homes for the relative coolness of Rock Creek Park. The thermometer read 97 degrees at 10 a.m. that day, hit 100 by noon, peaked at 103 at 4 p.m. and was still in the mid-90s by 8 p.m.

"Practically all government departments suspended business for the afternoon," said The Post. Acting Police Chief William Shelby even permitted police to remove their jackets and direct traffic in shirtsleeves, a remarkable surrender of sartorial propriety in that era.

Twelve years earlier, in August 1918, the city underwent a similar siege. The temperature reached 106 on Aug. 6, matching the record high that was equaled on July 19, 1930. The Post reported unofficial readings of 114 degrees on Pennsylvania Avenue NW and 121 degrees at the city courthouse.

"Much business about the city was practically at a standstill," said The Post. ". . . and crowds thronged the ice cream parlors. The roof gardens of the hotels were sought last night by those who could afford it and those who could not took refuge in the parks."

Though residents lacked air conditioning in those days, weather forecasters said yesterday, they also lacked the dense air pollution caused largely by heavy automobile traffic today.

"It's a trade-off," said one forecaster.