The National Park Service is planning to straighten one of Washington's enduring traffic bottlenecks -- the winding portion of 15th Street NW through the Mall -- and make other changes in an effort to cut car and pedestrian accidents in the area near the Washington Monument.

Under the park service plan, the curving, 80-foot-wide section of 15th Street will be made straight between Madison and Jefferson drives, the narrow streets that flank much of the Mall.

Michael Donnelly, the park service official coordinating the work, said the $1 million construction project will be done sometime in the year starting Oct. 1, although no date has been set.

He said the street realignment could take four months and that the road is likely to be closed during that time.

The National Capital Planning Commission, which oversees federal projects in this area, and the federal Commission of Fine Arts, the arbiter of esthetics for much of Washington, must give final approval to the park service's plan, but have already given their tentative go-ahead.

Donnelly said that while the road is being straightened, a larger parking area will be built alongside 15th Street for Tourmobile buses, which now have little room to drop off and pick up tourists visiting the monument.

He said the current winding four-lane roadway, while actually the same width everywhere as it passes through the Mall, "appears to narrow because [drivers] don't stay in their lane."

Moreover, Donnelly said, "Motorists [seeking information] tend to stop and ask almost anyone who looks official."

At the same time, he said pedestrians routinely jaywalk across 15th Street, which "makes for an unpleasant mix of people and traffic."

While precise totals on accidents on the 15th Street area of the Mall have not been kept, Donnelly said there have been numerous sideswipings by cars and "close calls all the time."

The 15th Street construction is part of a broader park service plan to improve safety around the Washington Monument and make it easier for tourists to get to the obelisk.

Donnelly said that two pedestrians have been killed in the last five years when they jaywalked across 14th Street on the Mall.

"As people move from the Capitol, the monument is such a target people just cross in the middle of the block," he said.

"We're trying to get people to walk across at the corners at Jefferson and Madison," Donnelly said.

The Mall, which is mostly level, slopes down toward 14th Street, but the park service plans to fill in the area with dirt, plant shrubs and construct a low limestone wall in an effort to entice pedestrians to cross the street at the Madison and Jefferson intersections.

Donnelly said the initial work on the Washington Monument grounds will start next month with the construction of two parallel walkways leading from 17th Street to the monument.

The $1 million project is being paid for by the American Society of Civil Engineers as a birthday present honoring last year's 100th anniversary of the completion of the monument.

By 1991, he said a new snack bar will be built at 15th and Madison streets and the existing Monument Lodge dismantled and reconstructed southwest of the monument. Seating space for 200 more tourists will be added to the 100 seats next to the monument.