As the wildfire season ramps up across the West, the U.S. Forest Service is adding bigger, faster planes to its fleet to fight the fires.

The forest service announced Monday that it has selected contractors to provide seven air tankers that fly faster and drop a larger payload of fire retardant than other planes in its firefighting fleet.

The agency will spend nearly $160 million over five years for access to several models of aircraft, including a converted DC-10 jumbo jet, which can carry about five times as much flame-resistant liquid as any aircraft in regular use. The cost is about double the amount spent in past years, but the planes are expected to provide better service, said forest service fire and aviation director Tom Harbour. They also require less maintenance.

Each of the planes can carry more than 3,000 gallons of slurry and fly faster than 350 mph, the Forest Service says. The DC-10 can hold as much as 11,600 gallons.

The newer planes are set to join the aging fleet of eight large tankers, mostly Korean War-era submarine chasers, known as P2Vs, which can fly about 165 mph and hold about 2,000 gallons of fire retardant. Several such planes have been involved in fatal crashes recently, reducing the size of the fleet.

Just when the new tankers would start fighting wildfires is not clear. Unsuccessful bidders have a chance to file protests challenging the choices, and various factors will determine how long that takes, the Forest Service said.

Forest Service Chief Tom Tidwell said in a statement it is "critical" to complete the effort "as quickly as possible as we face the prospect of another challenging wildfire season with a dwindling legacy air tanker fleet."

Sen. Mark Udall, D-Colo., urged bidders not to delay the process by filing protests, which prevented the Forest Service from adding new planes last fire season.

Last week, the first 2013 fire season outlook from the National Interagency Fire Center said a dry winter and a warm spring put the wildfire potential above normal across the West.

The effort to boost the air tanker fleet comes as the Forest Service enters fire season with 500 fewer firefighters and 50 fewer fire engines than last year due to budget cuts mandated by Congress under what is known as the sequester. The firefighting budget stands at about $2 billion.

Forest Service Fire and Aviation Director Tom Harbour said the department will compensate by repositioning crews and equipment to areas of the highest risk.

The contracts announced were:

— Minden Air Corp., of Minden, Nev., for one BAe-146.

— Aero Air LLC, of Hillsboro, Ore., for two MD87s.

— Aero Flite Inc., of Kingman, Ariz., for two Avro RJ85s.

— Coulson Aircrane (USA) Inc., of Portland, Ore., for one C130Q.

— 10 Tanker Air Carrier LLC of Adelanto, Calif., for one DC-10.