A guick dash of silver paint by the mechanic on the car's underside and voila, a new Silver Streak (brand) transmission. Customers charge, $300.

Automobile repair frauds - like this egregious example discovered in Philadelphia - together with shoddy and unnecessary work continue to cause more complaints than any other single consumer product or service. Yesterday the House Commerce subcommittee on consumer protection began the first of four hearings devoted to finding ways to reduce auto repair complaints and costs.

Chairman Bob Eckhardt (D-Tex.) began the proceedings with a few sobering statistics: the cost of auto NHTSA report however: diagnostic inspection. Inspections covering emissions, fuel economy and noise as well as safety were found in demonstration maintenance and repair since 1972 has risen at an annual rate of 8.4 percent, more than the inflation rate and the cost of living index. Last winter, the urban working family spent as much (19.3 percent) of its budget on private transporation as it did on food. The car's care cost more than education or clothing for the family's male members.

Last May, the National Highway Traffic Safety Administration estimated the cost to consumers of improper or unneeded auto repairs and proper or unneeded auto repairs and maintenance practices at $20 billion annually. This amounts to more than half of the estimated $50 to $55 billion in after-purchase car costs in 1978. (This figure includes warranties, accessories and do-it-yourself repair kits, as well as professional maintenance and repairs; it excludes fuel.)

When the NHTSA report was published, many press accounts omitted the fact that half of the $20 billion cost stems from owners' failure to maintain or repair their vehicles as indicated by the manufacturer and from automobile designs that place a priority on ease of manufacture over ease of repair and diagnosis.

Industry representatives yesterday jumped on this misunderstanding in an attempt to discredit the entire report. William A. Raftery, president of the Motor and Equipment Manufacturers Association, said an industry-wide task force was studying the data. He declined to offer any figures of his own in place of what he termed the "grossly inflated and unsupportable $20 billion figure."

There was considerable industry support for another aspect of the programs to benefit the consumer. The report recommended using separate businesses for inspection and repair. Diagnostic reports, prescribing specific repairs, for example, reduced the rate of unnecessary repair of cars by 50 percent. NHTSA director Joan Claybrook said the agency will do a study next year on the means for financing diagnostic centers.

The NHTSA report also recommended vehicle standards that can reduce maintenace requirements; Claybrook said manufacturers have not yet given high priority to designing cars that are easier to diagnose and repair.

Most witnesses suggested the federal government should not involve itself too much, but rather be a catalyst for state action.

California was the first state to set up a Bureau of Automotive Repair, back in 1971. Yesterday its deputy chief, Douglas Laue, testified that it had processed 26,660 complaints and obtained $658,864 in refunds or rework. And, when it passed a regulation saying mechanics had to prove a car needed ball joints, sales of ball joints reportedly fell 85 percent overnight.