WASHINGTON – Senators concerned about the hit that Navy shipbuilding took in the president’s budget suggested Thursday using a $10 billion war reserve fund to help make up for the shortfall.

The Pentagon is asking for money to build five new warships, down from six in the current budget, in President Bush’s proposal for next year.

Defense officials estimate that about 20 ships go out of service annually. Several naval officials fear that if the Pentagon keeps to its recent pattern of building only five or six ships a year, it will lose more ships to attrition than it gains from construction. The result would be a shrinking fleet.

“The impact of the current procurement rate goes beyond force levels,” Adm. Vernon Clark, chief of naval operations, said in his testimony before the Senate Armed Services Committee. “It adversely affects the stability of our defense industrial base, and we are paying a premium in program cost due to the small number of units being built.”

Clark testified before the panel along with the chiefs of the other military services.

Sen. Susan Collins said it didn’t make sense for the president’s budget to call for a $48 billion defense increase for next year, the largest in two decades, when a critical need such as shipbuilding gets shortchanged for a third consecutive year.

“We cannot continue to defer this problem year after year,” she said. “We’re just getting deeper and deeper in the hole.”

Collins suggested dipping into a $10 billion reserve fund Bush has proposed to help pay for the construction of additional ships. The committee’s ranking Republican, Sen. John Warner of Virginia, also supported the idea.

The president proposed the $10 billion account as a contingency fund he could spend without further congressional action for military operations against terrorism.

Prospects for congressional approval seem dim, however. The contingency fund has been called a slush fund by some Democrats and drawn bipartisan criticism for the lack of say Congress would have over it.

The administration is proposing to spend $6.5 billion to build two Arleigh Burke-class destroyers, one Virginia-class attack submarine, one amphibious transport ship and one logistics ship.

The budget also adds $1 billion to convert four nuclear-armed Trident submarines to carry non-nuclear cruise missiles.

Defense Secretary Donald H. Rumsfeld, in explaining his decision not to speed up shipbuilding, told Congress last month that the average age of the current fleet is low enough to merit waiting.