After 40 years of rugged service, the venerable Jeep is about to be replaced with the High-Mobility Multi-Purpose Wheeled Vehicle, or, as the Army affectionately calls it, the HUMMvee.

Two years ago, the Pentagon decided that it needed to replace its aging fleet of 114,000 Jeeps and light trucks. It said the Army, Air Force and Marines could save money and improve efficiency by using standard vehicles for non-combat tasks and developing a combat replacement for the Jeep that would be larger, faster and more versatile.

Last month the Army signed a $690 million contract with General Motors for 53,000 light-duty Chevrolet trucks and four-wheel-drive Chevrolet Blazers to meet some of its non-combat needs.

General Dynamics, Teledyne Inc. and Jeep-maker American Motors are competing for the HUMMvee contract, worth an estimated $2.2 billion.

In April each company delivered 11 prototypes to the Army for testing and the Pentagon plans to select a contractor after December to build at least 100,000 of the vehicles.

Like the Jeep, the HUMMvee will have to be able to accelerate from zero to 30 mph in six seconds and will have to be able to climb a 60-degree grade. But the HUMMvees also must run on flat tires for at least 30 miles, have a fuel tank that won't rupture if a half-pound of dynamite goes off under a tire, and get 26 miles per gallon on diesel fuel, compared with the Jeep's 19.

They also must have automatic transmissions because, the Army said, many new recruits don't know how to drive stick-shifts.

The biggest advantage of the HUMMvees, according to the Pentagon, is an adaptable chassis that will allow it to be troop carrier, ambulance, anti-tank missile launcher and about a dozen other specialties. Because it is so adaptable, the Army said it will be able to elimintate its half-ton "mule" truck and the quarter-ton "Gamma Goat" truck along with the Jeep.

The Pentagon doubts, however, that any of the companies will show off their HUMMvee the same way that Willys-Overland rolled out its prototype Jeep. A test driver gave members of Congress rides up and down the steps of the Capitol to demonstrate the vehicle's climbing skill.