Near the heart of downtown Washington, almost hidden away from residents and tourist crowds, lies the natural calm of a wilderness preserve: Theodore Roosevelt Island.

That calm will be broken this weekend, however, when the 88-acre forest preserve on the Potomac River becomes the site of a celebration honoring the 125th anniversary of its namesake's birth.

Less well-known than other area monuments to American presidents, it receives few visitors--less than 100,000 people visited it last year, compared to the more than a million who visit the memorials to Washington, Lincoln, Jefferson and Kennedy.

To the president's great-grandson, Theodore Roosevelt IV, who lives on Long Island and works for a New York investment bank, that is a mixed blessing. While pleased that hordes of tourists do not invade the serenity of the island each year, he wishes that more visitors would enjoy it.

"I think it's the island terrific," said Roosevelt, who was present at the dedication of the park in 1967 and will speak at this weekend's ceremonies. "I wish we had something like it in New York City."

The island is largely covered by a dense undergrowth of English ivy and periwinkle as well as extensive stands of Japanese honeysuckle and native American poison ivy. It also boasts some 225 bird species.

The only access to Roosevelt Island is by foot over a bridge from a parking lot accessible by car from the northbound lanes of the George Washington Memorial Parkway. Eventually, a $750,000 pedestrian-bicycle bridge across the parkway will connect the existing foot bridge with Rosslyn. The bridge, originally slated to be built this summer, will be built next year.

The parking lot is expected to be closed Saturday for the anniversary celebration but the Park Service will provide continuous free double-decker shuttle bus service to the island from the North Pentagon parking lot from 11 a.m. to 7 p.m.