AJEWEL IN Washington's crown of cultural riches, the John F. Kennedy Center for the Performing Arts, under the energetic leadership of its president, Michael M. Kaiser, is preparing what would be the most ambitious expansion in its 32-year history. The plan calls for construction of a sweeping deck and plaza -- more than 17 acres in all -- that would cover the spaghetti works of concrete at the entrance to Interstate 66 east of the center, accommodate two new buildings dedicated to the performing arts and open a more hospitable gateway for pedestrians and bicyclists to a building that is disconnected from the city it serves by a tangle of forbidding freeways.

The dimensions and details of the project are the subject of a healthy debate. Local planners and some critics want a livelier plaza that would include more shops, restaurants, cafes and, possibly, housing, in addition to the amphitheater already envisioned in the center's architectural plans. But the debate may soon be moot: As it stands now, Congress has not designated a nickel for the Kennedy Center's expansion.

Of the project's $700 million price tag, $300 million would come from private funds to finance the construction of the two new buildings; the center has already raised about half that amount, including a $100 million gift from Catherine B. Reynolds, the arts philanthropist. The remaining $400 million, for the deck, plaza, and an array of roadwork, ramps, and pedestrian/bicycle trails, would come from the federal highway bill -- and that's the rub. The bill, a six-year colossus, is caught up in a three-way tug of war among the House, the Senate and the Bush administration. Competing versions range from a $256 billion plan favored by the White House to a $375 billion bill championed by some House conferees. None of them includes earmarked funding for the Ken- nedy Center, despite the efforts of Rep. James L. Oberstar of Minnesota, a longtime Ken- nedy Center ally and the ranking Democrat on the House Transportation and Infrastructure Committee.

That's a shame. The Kennedy Center rightly bills itself as a congressionally designated national showcase for the performing arts and a living memorial to the late president. One need not love the stodgy, undistinguished architecture of the original structure to see that it is also a vibrant, essential institution that draws 2 million visitors a year. But the center is badly in need of a fix to help absolve the original sin of its awkward setting by better integrating it with the Mall, the Lincoln Memorial, the White House, Foggy Bottom and the pedestrian pathway along the Potomac. The expansion plan holds out the promise of doing that and much more. By incorporating two major new buildings onto the plaza to house rehearsal, educational and exhibition space, the project would reinvigorate a world-class center for the performing arts and revitalize a congested, confused corner of the city.