The weatherman, whose predictions this summer of temperatures in the 90s with the humidity close behind have become as monotonous as they are forbidding, announced yesterday that a cold front from the north is bringing pleasant, sunny wheather to the Washington area. But it won't last.

The National Weather Service forecast calls for temperatures in the mid-80s with the relative humidity around 40 per cent today and Tuesday.

Jack Fuge, a forecast at the National Weather Service, said the cold front from New York and Pennsylvania will dissipate just south of the metropolitan area. The result will be a resumption of the hot, humid air being funneled through the pressure area stationed off the cost of South Carolina known as the Bermuda High.

Yesterday's official high temperature of 84 degrees recorded at National Airport shortly after noon marked second day in a row that the thermometer remained under 90 degrees.

Prior to Saturday, when the high was 86, the metropolitan area endured nine consecutive days of 90 degree plus weather. The record for continous days of over 90-degree temperatures was set in 1872, when the thermometer rose above the 90-degree mark for 18 days.

The lower temperatures over the weekend were accompanied by relatively smog-free air. The air quality index yesterday was 19, officially labeled "good quality" by the Metropolitan Council of Governments. On Saturday the AQT was 22.

Fuge, the whether forecaster, said the Bermuda Highs are high pressure areas that cover the western Atlantic from Bermuda to the east coast of the United States. He said they are common in summer and cause warm, humid air from the Carribbean and the Gulf of Mexico to flow up into the eastern United States.

The showers and thundershowers that dropped 1.2 inches of rain at National Airport yesterday forced the Maryland State Marine Police to suspend the search for the body of an unidentified man believed to have drowned in the Potomac River on Saturday near Hallowing Point. Md.

Authorities said that the man, believed to be and Alexandria resident about 29 years old, fell into the river from a 38- foot houseboat about 4:30 p.m. Officials said dragging operations would be resumed later.

The thundershowers did not prevent about 1.500 motorcyclists from riding along 14th Street NW to Pennsylvania Avenue and then on to Upper Marlboro to dramatize the need for motorcycle safety.

At the Washington monument, a spokeswoman reported that about 3.500 visitors had passed throught he turnstiles by late afternoon. She said this was fewer than on a normal summer Sunday and attributed it to the weather. But at Arlington National Cemetery almost 5,000 tourists were counted - average for this time of year, an official said.