The kind of rainstorms that drenched the Washington area this spring all but vanished last month, resulting in the driest July here in nine years.

Rain fell only four days in July. In one 15-day stretch there was no precipitation. For the entire month, the metropolitan area received only 1.78 inches of rain, less than half the normal amount for July, and the lowest for the month since July 1974, when 1.15 inches of rain was recorded, according to the National Weather Service.

Accompanying the drought-like conditions were temperatures of 90 degrees or more on 20 days in the month, scorching area lawns, damaging crops and driving up electric bills.

But this could change in August, which although is hot, is normally the wettest month of the year, largely because of intermittent, intense thundershowers.

The National Weather Service's preliminary forecast for the next two weeks calls for rain to occur more frequently than in July.

But if that prediction is wrong and the dry spell persists, the area water table could reach dangerously low levels and more severe crop damage could occur, Jeff Bowman, a National Weather Service meteorologist, said yesterday.

"Just by having that shot of rainfall in the spring, helped us tremendously over the dry spell we've had in July," Bowman said, but "if we continue one month of this, we could be hurting quite substantially."

Area farmers would be hit hardest by a prolonged drought, Bowman said, adding that corn and other crops that should have been ready for picking in July withered from the heat and drought.

Another immediate effect of the lack of rain and sweltering temperatures has been to cause some area lawns to turn brown.

"The high temperatures act like a big hose sucking the moisture out of the ground and trees, and that further depletes the ground moisture," Bowman said.

Bowman said the cause of this year's hot, dry spell is a high-pressure system that has engulfed and baked the Midwest for weeks. That system, advancing on westerly winds, has settled over the Washington area, and has blocked out southerly, moist winds from the Gulf of Mexico and the Atlantic, which normally sweep into this area and bring rain with them.

In addition, Bowman said, the high-pressure system has served to trap moist air close to the ground, preventing it from rising into the atmosphere where it would help form clouds that would in turn lead to rain.

In contrast to the current dry spell, the months of March, April, May and June had heavy, almost constant rains, particularly on weekends.

It rained on Saturday or Sunday or both days on 14 of the 17 weekends from March through June, Bowman said.

Nearly two feet of rain fell from March through June, which was more than 10 inches above the normal rainfall for this period. The heaviest rain came in June, when showers poured more than 7 inches of rain on the Washington area.

For the first seven months of 1983, nearly 30 inches of rain fell. The normal annual accumulation of rain in Washington is 39 inches.

Bowman said this spring's infusion of rain brought the area's water table back to normal levels for the first time in three years.

In 1980, the water table was 10 inches below normal, in 1981, it was eight inches below and in 1982, it was three inches below normal, Bowman said.

So far this year, he said, the water table is more than seven inches above normal. "Of course," Bowman said, "we could erase all that if we go through another dry month and a half."

Although temperatures were up this July, the highest temperature was 99 degrees on July 17, they were still below those recorded in July and August 1980, the hottest summer on record, Bowman said.

During the summer of 1980 the thermometer hit 100 degrees or higher three times in July and twice in August. The highest temperature was 103 degrees, which was recorded on July 16, 1980.

"That was a summer to remember," Bowman said.