WASHINGTON — The powerful Senate Appropriations Committee agreed Wednesday to block the Defense Department from consolidating destroyer construction at a single shipyard, disrupting a proposal that threatens the future of Bath Iron Works in Maine. The Senate panel included a provision in an $81 billion bill for Iraq and Afghanistan that would prevent the Pentagon from spending any money on changing from two shipyards to one.

The provision is significant because the bill will be approved quickly and the full Senate is likely to adopt the committee version.

While sounding innocuous, the provision - if successful - would effectively block the Pentagon from consolidating destroyers at either BIW or Ingalls Shipbuilding in Mississippi, as the Navy secretary has proposed.

However, the House version of the emergency spending bill doesn't feature a similar provision, so it must survive a conference between the chambers. President Bush's position is unknown, although Maine Sen. Susan Collins, a Republican, said she has been lobbying White House officials vigorously.

"This is strong, effective language attached to a powerful train that is moving forward toward the president's desk," said Collins, a member of the Armed Services Committee. "This is great news for Bath Iron Works and its employees. It is not the final step, but it is a very significant step forward and a very positive one."

Plans to consolidate shipbuilding roiled Maine and Mississippi because of the jobs at stake with the next generation of destroyer called the DD(X). BIW is Maine's largest single-site employer, with 6,200 workers. Ingalls, which has 12,000 workers, won the competition to design DD(X), but the yards have split construction of current destroyers for years.

Lawmakers and industry officials in both states have lobbied to keep both yards.

"I have long believed that it is in the interest of both the Navy and the nation to maintain the industrial capacity of two shipyards," said Sen. Olympia Snowe, R-Maine. "There are many of us in Congress who understand we continue to live in an uncertain and dangerous world. We need to have all the tools in our military arsenal to be prepared for any potential future threats."

But Navy Secretary Gordon England told the Senate Armed Services Committee a month ago that the government could no longer afford the luxury of subsidizing one yard by dividing the construction because the overhead adds an estimated $300 million to the cost of each ship.

Besides consolidating construction, the administration has also proposed cutting destroyer construction through 2011 from 12 ships to five.

Collins and Snowe were among 20 senators who sent President Bush a letter urging a continuation of two yards. The group also got language in the Senate version of the budget blueprint, which is still in negotiations with the House, that would prevent a move to a single shipyard.

But that was a non-binding resolution, while the language in an appropriations bill is considered much more powerful because it prevents expenditure of funds.

The provision states: "No funds appropriated or otherwise made available by this Act, or by any other Act, may be obligated or expended to prepare for, conduct, or implement a strategy for the acquisition of the next generation destroyer DD(X) program through a winner-take-all strategy."

The provision defines a winner-take-all strategy as building destroyers at a single shipyard.

Congress will approve the spending bill quickly because the funding is needed for troops in Iraq and Afghanistan.

But support for the provision could be weaker in the House than in the Senate, because neither of Maine's congressmen serves on the appropriations or armed services committees.

The White House position will become clear when the Senate debates the bill on the floor because there will be a "statement of administration policy" that outlines what it supports or opposes in the bill.

"This very firmly says to the Pentagon that you should not change our acquisition strategy," Collins said. "It would jeopardize the industrial base. It would be disastrous for our national security to rely on a single shipyard for these vital new destroyers."