IN A VICTORY of decent taste and common sense, the House last week rejected plans to prop up the sagging West Front of the U.S. Capitol with a disfiguring marble extension. The 325-to-86 vote was an unequivocal reversal of an earlier decision by the House Appropriations Committee to spend more than $70 million for an extension. By joining with the Senate, which has already voted for restoration rather than extension, the House has now paved the way for the long-overdue repairs.

Aided and abetted by the architect of the Capitol, George M. White, proponents of the extension argued that the plan wouldn't demean the historical significance of the oldest remaining portions of the Capitol building. Quite the contrary. The sandstone west face would be preserved for all time--you just wouldn't be able to see it. Instead, it would be entombed behind a 31-foot marble extension providing hideaways and other conveniences for status- hungry congressmen and their constituents.

These preservationists from the we-had-to-destroy-it-in-order-to save-it school argued, moreover, that the cost of the addition would be only a few million dollars more than the cost of shoring up and refurbishing the old facade. Many congressmen found that estimate implausible, coming as it did from Mr. White, an architect whose projects in the past have led to monumental cost overruns. Their suspicions were not allayed by the discovery last week that, owing to an "inadvertent oversight," Mr. White's new plans would have required further modifications since they left only a seven-foot walkway where the Capitol's west terraces now sweep.

Having decided to do the right thing, Congress should waste no more time. It should get the best advice possible on how to proceed--and we do not put Architect White's counsel in this category--and start the restoration work quickly, before the congressional urge to conquer more office space reasserts itself.