A 13-year-old Prince George's County youth was missing and presumed drowned last night after falling into the rushing waters of a swollen creek as the Washington area was deluged by almost two inches of rain.

The youth was attempting to cross Henson Creek in a park in the Oxon Hill area about 6:15 p.m. when he slipped and plunged into the waters, according to the Maryland National Capital Park Police. Police, who declined to identify the youth, said a search for his body would resume today.

The 1.94 inches of rain recorded at National Airport by midnight made yesterday the rainiest day of a month that is celebrated for its showers. More than a dozen roads and streams, particularly in Montgomery, Fairfax and Prince William counties were blocked by high water and closed at times as nearby streams overflowed their banks.

Area police reported a substantial increase in the relatively minor accidents that appear to be a consequence of inclement weather. One traffic fatality was reported on Rte. 1 near Fort Belvoir in Fairfax County late last night, but it was not immediately known if the accident was weather-related.

A 17-year-old Howard County youth was killed near Clarksville on Rte. 32 when his car spun out of control and into the path of a dump truck, according to county police. They said James D. Shenk of Highland was driving on worn tires and apparently lost control of his car as a result of the heavy rain.

In addition to snarling downtown traffic in spots, yesterday's daylong downpour created ponds on lawns and puddles in gardens, boosted umbrella sales and prompted the National Weather Service to issue flash flood warnings for storm sewers and small streams across the metropolitan area from Prince William County north to Howard and Montgomery counties.

Streams and rivers throughout the area were described last night by the weather service as "hazardous." The Monocacy River was expected to crest about six feet above flood stage in Frederick, Md., at 1 p.m. today. In Washington, the Potomac River was expected to be "just nudging flood stage" Sunday at Little Falls, according to weather service forecaster Leo Harrison.

During the first 15 days of April, it has rained 11 of them. March gave the area 15 days of showers and a total of 4.84 inches of rain. February had nine wet days, a total of 3.09 inches of rain.

As the heaviest rain began moving out of the area last night, forecasters said today might begin the first dry weekend here since March 12. Today is expected to be partly cloudy, tonight clear and tomorrow sunny.