July 1987, a month without precedent here for the oppressive regularity with which it provided steamy, searing days of at least 90 degrees, ended yesterday as it began, with a high temperature in the 90s.

The high recorded at National Airport was a sticky 95 degrees, providing a sweat-soaked finish to a month that began on a day when the mercury topped out at 90, and included a record total of 24 days that were at least that hot.

In addition to staking a claim to being Washington's hottest month, based on its number of 90-degree days, July appeared to match the all-time record for average high temperature. According to unofficial calculations, the average of the daily highs was 92 degrees.

No July recorded has been so hot. The old July record was set 105 years ago, when the average was 91.9 degrees. The 92-degree figure matches the all-time mark set in August 1980, a month of legendary heat, when the mercury hit the 90s on 22 days.

August, as well, is expected to be warmer than normal, according to the National Weather Service, but its first two days at least are expected to provide relief from this summer's theme of thermal excess.

A cool front drifted southward toward the Washington area yesterday evening, according to Weather Service forecaster Bob Oszajca. It remained north of the area most of the day, keeping temperatures in the 80s in Baltimore and Wilmington, Del. Highs here are expected to remain in the 80s today and tomorrow.

As the front approached, scattered heavy thunderstorms burst over parts of the Washington area during the evening, bringing brief but torrential rains.

Based on unofficial figures, July brought about 2 1/4 inches of rain to National Airport, where the average figure is 3.88.

The Fairfax County Water Authority said the 875,000 people it serves in Northern Virginia appeared to comply with conservation requests, but said the odd-even plan for outside water use -- based on house numbers -- probably will continue through the season.

Demand has declined from a record 153 million gallons of water on July 22, to an estimated 121 million a day.