The National Capital Planning Commission is expected to approve final plans today for the $750,000 pedestrian and bicycle bridge linking Rosslyn and Theodore Roosevelt Island.

The new bridge, planned for a decade and under review by federal and local agencies for more than two years, will provide Arlington County with its first public access to Roosevelt Island park and to the Potomac River. The county has been landlocked since the construction of the scenic federal parkway in 1934.

National Park Service officials this week promised to link the new bridge with the popular George Washington Memorial Parkway bicycle trail by next fall, when construction of the new bridge is expected to be completed.

"We expect the new bridge and the trail will be used extensively by commuting bicyclists and recreational cyclists and pedestrians," said Park Service spokeswoman Sandra Alley. The 14-mile parkway trail, which attracts more than a million people a year, stretches between Mount Vernon and Memorial Bridge, about one-half mile below Roosevelt Island.

The new bicycle-pedestrian bridge, to span the parkway just south of Key Bridge, will connect with the new $13 million Rosslyn Plaza over I-66, expected to get under construction next spring but possibly take two years to complete. The plaza is to be constructed largely on decking over I-66. The steel girders for the plaza deck were completed last year.

The bridge and the giant plaza will make a short walk to Roosevelt Island for thousands of Rosslyn office workers, as well as Georgetown residents across Key Bridge. The 88-acre island, opposite the Kennedy Center, is an urban wilderness memorial to the 26th president.

The bicycle-pedestrian bridge is being funded with Arlington, state and federal funds as a regional project, since it not only will open up public access to Roosevelt Island -- now accessible almost exclusively by automobile from the parkway -- but will link up the area's longest and most popular bicycle trails.

The NCPC staff has recommended approval of the bridge design, which has been somewhat modified and relocated since the federal planning agency approved rough plans for it in 1982. The latest design is "a lighter and lower structure" that will not detract "from the magnificent views of Georgetown and the Potomac River," the staff report states.

In fact it will make those magnificent views available to pedestrians and cyclists for the first time and is part of the long-range federal comprehensive plan for Washington-area open space and parks.

With completion of the bridge, cyclists will be able to ride from Washington's Rock Creek Park bicycle trail or from Mount Vernon all the way to Leesburg, since the I-66 bike trail connects with the Washington and Old Dominion Railroad Regional Park (the W&OD Trail) of the Northern Virginia Regional Park Authority. The paved W&OD trail now extends to Sterling Park in Loudoun County. In a few years it will reach Purcellville near the Blue Ridge Mountains.

The federal Fine Arts Commission approved the final design of the 12-foot wide concrete and steel bridge last week.