WASHINGTON — The top leaders in both parties on the House and Senate Agriculture committees have agreed to a one-year extension of the 2008 farm bill that expired in October, a move that could head off a possible doubling of milk prices next month.

Senate Agriculture Committee Chairman Debbie Stabenow, D-Mich., indicated the House could vote on the bill soon, though House leaders have not yet agreed to put the bill on the floor. In addition to the one-year extension that has the backing of the committees, the House GOP is also considering two other extension bills: a one-month extension and an even smaller bill that would merely extend dairy policy that expired Tuesday.

Expiration of those dairy programs could mean higher prices at the grocery store within a few weeks. Agriculture Secretary Tom Vilsack said Americans face the prospect of paying $7 for a gallon of milk if the current dairy program lapsed and the government returned to a 1948 formula for calculating milk price supports.

A spokesman for House Speaker John Boehner said Sunday that Republican leaders had not decided how they would proceed on the farm extension, though a vote could come as soon as Monday. Boehner has pushed back on passage of a new five-year farm bill for months, saying there were not enough votes to bring it to the House floor after the House Agriculture Committee approved it in July. The Senate passed its version of a farm bill in June.

The prospect of higher milk prices has motivated some action. The bipartisan extension also includes disaster assistance to farmers affected by a lingering drought this year, along with extensions to other farm programs that expired in October.

Instead of just extending current dairy policy, the extension bill includes an overhaul of dairy programs that was included in both the Senate and House committee bills. The new dairy programs include a new, voluntary insurance program for dairy producers. Those who choose that new program also would have to participate in a market stabilization program that could dictate production cuts when oversupply drives down prices — an idea that hasn’t gone over well with Boehner.

In July, he called the current dairy program “Soviet-style” and said the new program would make it even worse. Large food companies that process and use dairy products have backed Boehner, saying the program could limit milk supplies and increase their costs.

Stabenow blamed Boehner for getting to the point where an extension is the only option. “The lack of action by the House Republican leadership has put us in a situation where we risk serious damage to our economy unless we pass a temporary extension,” she said.

One of the reasons Boehner has balked at bringing up a farm bill is disagreement within his caucus over how much money should be cut from food stamps, which make up roughly 80 percent of the half-trillion-dollar bill’s cost over five years.

House Agriculture Chairman Frank Lucas, R-Okla., has unsuccessfully pushed his leadership for months to move on the legislation despite the disagreement over food aid.

On Sunday, Lucas said he hoped the extension would pass both chambers quickly as GOP leadership mulled their options.

“It is not perfect — no compromise ever is — but it is my sincere hope that it will pass the House and Senate and be signed by the president by Jan. 1,” he said.