IT INDUCES A SINKING sensation to learn that the congressional leadership has endorsed yet another inane plan to extend the Capitol's West Front. The plan, you'll be sunk to hear, is in the best tradition of aesthetic mongrelism under which an earlier leadership group architecturally despoiled our nation's most venerated site. Ever since the 1950s, congressional leadership, functioning as the "Commission for the Extension of the Capitol," has lead a crusade to get more Capitol office space by defacing the West Front - as they did the East Front - with a white marble addition that would alter the building's proportions. And, in the process, it would cover the last remaining soft sandstone portion of Dr. William Thornton's original Capitol. This wrongheaded expansion scheme finally met defeat in 1973 (it then would have cost $58 million) as the result of an impasse between the House (which was for it) and the Senate (which was against it). After years of hassling, the West Front had come through undistorted, and, as we observed at the time, "historic preservation, fiscal prudence and common sense all seem to have prevailed."

But now a new extension plan is resurgent, supported by the same old arguments. Everybody agrees that the sandstone facade of the West Front is deteriorating and needs repair (back in the 1790s they used sandstone as an economy measure). The repair could be done by drilling 57,000 small holes in the facade to pump in a wall-strengthening cement grout, a plan that would now cost $45 million, Capitol Architect George M. White estimates. But if you're going to have to spend that much anyway, the proponents contend, why not add $10 million more and have a whole new West Front - with different proportions - and get 25 per cent more office space (which is in particular demand by House members)? The sandstone facade would be preserved, it is reasoned, but it would lie deep inside a new West Front. The flaw in this reasoning, of course, is that, as Robert Burley of the American Institute of Architects said at recent hearings, "any extension or concealment of the West Front would be detrimental in terms of the historic significance, the architectural integrity, the public image and the symbolic impact of our nation's most important public building." Admittedly, the proposed new extension would be a bit less damaging aesthetically than its monstrous predecessor. Under the old 80-foot extension proposal, Frederick Law Olmstead's sweeping terraces facing the Mall would have been removed and rearranged. The new plan, which extends 19 feet in some places and 60 feet in others, spares the terraces.

Even so, we believe this nonsense should stop. The "Commission for the Extension of the Capitol" should restrain its lust for architectural disfigurement and get on with its real duty: the repair and restoration of the existing West Front, parts of which are now supported by unsightly heavy timbers. Three times in the past four years the Senate has voted to do just that, and the proposal has been shot down by the space-hungry House each time. The responsible action for congressional leaders would be to proceed with repairs that should have been done years ago - at a fraction of present costs.