Everyone has a horror story about the car. Self, neighbor, sister or someone has "had it in the garage 17 times for the air conditioning . . ." or "put a new transmission in after ruining the engine by just turning it on, and only 650 miles . . ." or "paid the dealer $379.21 to adjust the power steering."

No douubt the stories are true but, in general, cars built during the past few years are strikingly longer lasting, and require a pleasurably less regular maintenance.

And the 1978 model cars out within the month will continue the trend toward markedly longer intervals for costly normal maintenance such as tuneups and oil changes.

Taking the biggest step on the 1978s and announcing it publicly last week was Ford Motor Co. The company's four-and six-cylinder engines powering '78 models require a change of oil only every 10,000 miles.

They need tune-ups even less often.

Ford's '78 cars eith most six-cylinder engines and all four-cylinder engines with automatic transmissions need the tune-up at 20,000-mile intervals. For four-cylinder engines with manual transmissions, all V6 engines and most V8s, the tune-up interval is 30,000 miles.

According to Chester V. Barion, general manager of Ford's parts and service division, ""on more than 30 line items, service schedules have been eliminated or extended during the five-year period" such changes usually are measured on.

The Ford executive said the frequency of scheduled maintenanccce pealed with the '73 models at Ford and, in terms of dollaars, the reduction since then represents "major strides."

Scheduled maintenance cost s for most four-cylinder Ford cars over 50,000 miles are three-fourths less, Barion said. For '78 Ford V8 engines, the scheduled maintenance costs over 50,000 miles of driving should be $143 - compared with $564 for the 1979 V8.

Chevrolet touted a $400 reduction in comparable costs for its 1975 models and since then has been cuttings its maintenance costs slowly in a less dramatic fashion.

Chryler Corp. requires 7,50000-mile perreiods with the '77 models. Insiders at the No. 3 auto maker say they're looking for 10,000-mile periods with the '79 models.

How have the longer periods between regular maintenance come about?

A variety of reasons! Uleaded gasoline puts less "gunk" around the operating parts; high-energy electronic ignitions are simply better than the traditional points and condensor-arrangment; and there have been some deramatic improvements in the oils and greases used in automobiles.