Two persons disappeared and were presumed drowned in the Potomac River yesterday evening after swimming in what was described as high and fast flowing water below Great Falls.

The incident occurred several miles upstream from where two Navy men drowned nine days ago in a canoe accident.

A bright, sunny afternoon with temperatures in the 80s brought many swimmers to the river yesterday at the place where the apparent drownings occurred, and a U.S. Park Police helicopter had just flown overhead to order them over its loudspeaker to get out of the water.

"We know it's dangerous," a park police dispatcher said last night.

The drownings occurred at a spot in the river known as Catfish Hole, which usually is regarded as relatively free of the foaming turbulence characteristic of the Potomac below Great Falls, according to Lt. John Harris of the Cabin John fire department.

However, the rains and showers that fell earlier last week and made yesterday's sunshine particularly attractive, swelled the river and increased its hazards, Harris said.

Authorities said three swimmers, including at least one female, were involved in yesterday's incident. They were in the river opposite the Old Angler's Inn about 5:50 p.m. when the female called for help and another of the swimmers, a male, went to her aid.

Both disappeared. The third swimmer emerged safely from the river and reported the incident, according to the Montgomery County fire department.

At least three rescue boats joined in a search, but efforts to find the two missing swimmers were abandoned because of high and swiftly flowing water, and both were assumed to have drowned, fire officials said. The two had not been identified as of late last night.

In the May 30 incident, two Navy seamen were drowned in a canoeing accident near the Little Falls Dam, in a section of the river that reportedly has claimed eight lives in the past five years.