Washington ? The Constitution must be amended to ensure the continuity of government in case Congress is wiped out by a terrorist attack, a blue-ribbon bipartisan commission will recommend today.

If a Sept. 11-like attack destroyed Congress, the current system of holding special elections to fill vacancies in the House of Representatives would take too long — an average of four months, depending on the state — the 15-member panel found after a yearlong study.

Governors currently fill U.S. Senate vacancies, but without an amendment allowing similar temporary appointments to the House until elections could be held, the nation could have no functioning Congress in a time of great crisis.

The doomsday scenario that the Continuity of Government Commission addressed might seem the stuff of a Tom Clancy thriller, except for what happened in the fall of 2001. According to two of the plotters, the fourth hijacked plane, which crashed in Pennsylvania, was headed for the U.S. Capitol. And the anthrax-by-mail attacks that shut down a Senate office building revealed another vulnerability of the nation’s legislature.

Enacting a constitutional amendment is a tortuous process, requiring a two-thirds vote by both houses of Congress and passage by three-quarters of state legislatures.

After a lengthy debate, commissioners agreed unanimously that an amendment was the only solution. Similar amendments were proposed in the 1950s and 1960s under the threat of nuclear attack, but never advanced.