At least two dozen people, including 19 stranded on two islands by fast-rising waters, were rescued from the Potomac River and its banks yesterday, and one man was swept away by swift current and believed drowned, authorities reported.

The rescues took place in the Great Falls area, not far from where the man was reported swept away shortly after 2 p.m.

The man was later identified by Montgomery County police as Alejandro A. Lucero, 23, of Herndon.

U.S. Park Police and Montgomery County fire officials said they searched for him after witnesses reported seeing him struggling in the rain-swollen river and screaming for help.

Full details about the incident and the rescues were not yet available late last night. Fire officials said they did not know if Lucero had entered the river to swim, or had fallen in.

So far this year, five people have drowned in the treacherous 11-mile stretch of river between Seneca Creek State Park and Chain Bridge. Last year, 14 people drowned -- the highest number on record and nearly three times the yearly average for the past 10 years.

Authorities said helicopters, canoes, and boats were all involved yesterday in the effort to pluck stranded persons from spots identified as Sherwin, Rocky and Offutt Islands in the Potomac near Great Falls.

Montgomery County fire and rescue officials said a total of 19 were taken off Rocky Island and Sherwin Island, after the rising river cut off access to shore.

In addition, a park service official involved in yesterday's large scale rescue efforts said five persons were removed from Offutt Island by Park Police helicopter.

There were also reports of several other persons being rescued from a spot near the Great Falls Tavern observation deck by Park Service rangers with ropes.

Montgomery county fire department spokesman Sgt. Robert Harding said the people stranded on Rocky and Sherwin islands apparenly ignored signs warning against going onto the rocky outcroppings north and south of the larger Bear Island.

"Evidently, you can usually walk out there," Harding said. "But due to the rain, the river is doing crazy things."

The increased Potomac River flow was fed by heavy rains that fell Friday near the Potomac and its tributaries in West Virginia, according to forecaster Charlie Chilton of the National Weather Service. The 4.7 inches of precipitation that was recorded at one such location, he said, was more rainfall than the Washington area usually receives in the month of May.

All of the unidentified people rescued from the islands were unhurt, Harding said.

Harding said that the search for the missing man was suspended because the Sandy Landing area of the river where he disappeared -- south of the falls -- is "inaccessible" to rescue equipment.

"They go out and they look the best they can, and that's all they can do," Harding said.

As on previous weekends when such accidents have occurred, hundreds of picnickers lured by balmy weather streamed into the park yesterday, many attracted to the stretch of river that combines the wilderness dangers of high cliffs, white water and a waterfall with cold water temperature and two dangerous dams.

Most victims of the turbulent currents have been boaters, rock hoppers, swimmers and fishermen who ignored the posted warning signs.

The river claimed its last victim just over a week ago when a 16-year-old Kensington girl slipped off the rocks near Rocky Islands and drowned.

Last week federal and state officials told a congressional subcommittee that stricter regulations and enforcement are needed to help prevent Potomac River drownings.

"The public must become more sensitive to the risks of a summer canoe trip or even a casual jump out to a shoreline rock," said Rep. Michael D. Barnes (D-Md.), chairman of the House District of Columbia subcomittee on government operatins and metropolitan affairs.

The National Park Service has already instituted foot patrols along the shoreline and is increasing boat patrols to catch illegal swimmers and boaters. Maryland officials plan to ask the General Assembly to give the National Park Service authority to enforce state regulations on the river.

U.S. Attorney Elsie L. Munsell has asked the eight active U.S. District Court judges in the Eastern District of Virginia for a court order that would force anyone arrested entering the Potomac from parkland to appear in court. Currently, the maximum penalty for this offense is a $500 fine and six months in jail. J. Frederick Motz, the U.S. attorney for Maryland, has filed a similar request that would affect those who enter the river from the Maryland side.