Thirty Ford Motor Co. dealers in the Washington area are offering a new, no-cost "lifetime guarantee" on their repair work on Ford cars and light trucks, excluding parts that wear out in normal use.

The guarantee program, which is being tested by Ford in several cities in the country, is intended to increase the service side of dealer business. For many dealers, profits from parts and service work have been a crucial crutch during two years of depressed new-car sales. Three Washington-area dealers chose not to take part in the program, presumably because they don't think they need it, Ford officials said.

Chet Barion, general manager of Ford's domestic parts and service business, said that the guarantee is offered without charge to owners of new and used Ford cars and trucks who bring them to participating Ford dealers for repairs.

An owner whose transmission failed, for example, could have it repaired -- paying the customary charges for parts and labor -- and the dealer would pledge to fix the repaired transmission for free if it ever failed again, as long as the motorist owned the car. The same guarantee applies to warranty repairs, except that the initial repair costs would be covered by Ford warranties.

The guarantee covers "virtually all functional parts and components," Ford said, including cooling and electrical systems, engine, transmission, steering, suspension, factory-installed options and dealer-installed accessories that fail in normal use.

The coverage doesn't include maintenance parts such as spark plugs, filters, windshield wiper blades, or brake linings and clutch facings that wear out in normal use, Ford said. Nor does it include batteries, paints, sheet metal and trim.

In addition, a motorist who needs repairs under the guarantee must bring the car back to the dealer who performed the original service work.

Ford and the 30 dealers are sharing the cost of the program, Barion said: Ford supplies the parts, the dealers provide the labor, and they split the advertising costs. If the program leads to an increase in service business of 3 percent to 6 percent a year for the dealers, it will pay for itself, Barion said.

The Washington area is the third to offer the guarantee. It was introduced this summer in Chattanooga, Kansas City and Cleveland. Ford wants to test the response of dealers and their customers before deciding whether to seek a nationwide guarantee program, Barion said.

Vincent Sheehy of Sheehy Ford in Marlow Heights said he has run a comparable program for the past five years. Its main advantage is in car sales, giving dealer an extra carrot to offer hesitant consumers, he said.