The fresh air and lower temperatures that brought relief from the weeks of heat and humidity this weekend are expected to keep things moderately pleasant, at least for the next few days.

Although the National Weather Service predicted increasing humidity with a good chance of thundershowers this afternoon, cool air expected to arrive here Monday night should result in pleasant days Tuesday and Wednesday.

The extended outlook for Thursday and Friday called for scattered showers on both days. Charles Archambault, a senior forecaster at the National Weather Service, said, however, that the area will be spared the uncomfortable temperatures and conditions which became routine most of this month.

Washingtonians, taking advantage of a high of 87 degrees with a relative humidity of 48 percent, returned to their familiar diversions on a pleasant midsummer Sunday afternoon.

At the National Zoo, hundreds of people picknicked in the shade of the oak and maple trees and occasionally looked at the animals.

"I enjoy watching the human animals as much as the four-legged animals," remarked Matilene Berryman. "People here are not in their guard. The only place they'd be more relaxed is in a pool."

The cleaner air seemed to invigorate people. Malcolm X Park was crowded with Frisbee players, strollers, agroup of footballers, and small children wading in the pools.

Others sat on the ground and took in the soft breezes blowing across the huge park. Several people said they had spent most of their free time lately indoors, avoiding the heat and humidity and remaining as close as possible to the air conditioners.

"This is the weather that we normally have in Jamaica," said Errol Gillette, a business student at Howard University, as he waited for his fiancee to come back from a stroll.

Asked if he preferred last winter's cold or this summer's heat, Gillette reflected and, not too convincingly, said he would opt for the heat.