Farm-state lawmakers have agreed to a one-year extension of the expiring farm law that, if enacted, would head off a possible doubling of retail milk prices to $7 or more a gallon in early 2013.

The extension would end a 32-month attempt to update farm subsidies dating from the Depression era, when farmers were crushed by low prices and huge crop surpluses, to meet today’s high-wire challenges of tight food supplies, high operating costs and volatile markets.

House Agriculture Committee Chairman Frank Lucas, an Oklahoma Republican, said on Sunday he hoped the legislation would be passed by Congress and signed by President Barack Obama by Tuesday to avoid higher prices for milk in grocery stores.