Federal and state officials yesterday told a congressional subcommittee that stricter regulations and enforcement are needed to help prevent Potomac River drownings. But they said that the deaths will never stop until canoeists, rafters, swimmers and rock hoppers understand the enormous dangers of the river.

U.S. Army Spec. Joseph D. Odell, the sole survivor of a 1984 rafting accident at Little Falls dam south of Glen Echo, reiterated that point. He testified that his rafting group chose to ignore the warnings of people along the shore who tried to wave them back, and the raft overturned.

The five other rafters died, despite the fact that everyone had on a life jacket and had taken care to brace themselves in the raft before hitting the falls, Odell said.

"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 subcommittee on government operations and metropolitan affairs. The subcommittee held oversight hearings yesterday on three aspects of the Potomac River -- safety, the continued growth of hydrilla plants in the water and potential flooding.

Federal and state officials said they are stepping up their activities on river safety, because of the alarming number of drownings on the Potomac, including 13 in 1984 and five this year. The latest victim, a 16-year-old Kensington resident, died Sunday when she fell off rocks into the river at Great Falls Park in Virginia.

Officials said that a 1982 analysis of Potomac drownings found that the "typical" boater who drowns is a 22-year-old man, and the typical swimmer who drowns is a male teen-ager, aged 16 to 19. As a result, Virginia and Maryland officials have since begun educational campaigns aimed at high school students.

The National Park Service has 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.

Maryland is also drawing up rules prohibiting boating within a certain distance of some dams on the Potomac, including one at Brookmont and the Great Falls Aquaduct. Boating is already prohibited within 200 yards of the Potomac Edison Co. dam at Williamsport, Md. Officials from the Army Corps of Engineers and Maryland said that warning signs and buoys along the river have been improved.

In other testimony, Col. Martin W. Walsh Jr., commander of the Army Corps Baltimore office, urged Congress to appropriate funds to allow the Corps to erect permanent flood control barriers in the District. He said if a flood equal in severity to those of 1942, 1936 or 1889 were to occur again, a number of important buildings would be under water.

Among those flooded would be the U.S. departments of Commerce, Justice, Labor, and Health and Human Services, as well as the southern portion of the Ellipse and the Vietnam Memorial. Congress approved the permanent flood control program in 1946, but since then the project has been inactive, Walsh said.

Walsh also predicted that there would be continued problems with hydrilla, an aquatic plant that has clogged certain parts of the Potomac. He said it is possible that the river area covered by hydrilla will increase from 600 acres in 1984 to 34,000 acres over the next 10 years.

Last week, the corps put barrier film material in the Old Town Yacht Basin in Alexandria to see if that would stop the spread of hydrilla. In June, the Corps will use divers with suction machines to selectively remove hydrilla in the Belle Haven Marina.

The Corps also wants to use the herbicide Diquat to kill much of the hydrilla, but Virginia and Maryland have opposed the idea.