John Hill took his car to a tire and auto service shop in Fairfax County to have the motor mounts changed. A mechanic installed the wrong mounts, and left the engine fan jammed so that it could not turn. The company refused to return the $48 Hill paid for the work, although another company confirmed that the first mechanic had made a mistake.

Outraged, Hill called the Fairfax County Department of Consumer Affairs. It took an agency employe eight months of investigation and mediation and 46 telephone calls to get Hill's $48 returned to him. Even so, Hill fared better than many car owners who report shoddy work or deceptive practices to one of the four government consumer agencies in Northern Virginia, a study of the agencies' records show. Consumer help is provided by Arlington County, Fairfax County, Alexandria and a state consumer branch office.

Many people never recover the money they pay for unnecessary or faulty work because current legislation does not protect them well enough, officials say. In fact, only those who can afford to join a private automobile association now get the kind of protection consumer officials think the state should provide by law.

Consumer agencies are backing two bills that will be considered when the state legislature convenes in January.

One, introduced by Del. Raymond E. Vickery Jr. (D-Fairfax) would license repair shops. Garages that flout the law would have their licenses suspended or revoked.

Another bill, introduced by State Sen. Charles L. Waddell (D-Loudoun) would require shops to give written estimates to customers who ask for them; a detailed written invoice when work is completed; return replaced parts to the customer, and notify customers of their legal rights. It would prohibit charges that exceed written estimates by more than 10 percent if the customer has not agreed to them, or charges for unauthorized repairs.

Both bills face tough sledding in the legislature, according to their sponsors. Vickery and Waddell say that legislators from the state's rural areas do not understand the urgency of the issue in the more densely populated parts of the state. The bills also have come under strong attack from segments of the automotive repair industry.

No one knows how much Northern Virginians annually pay for faulty or unnecessary auto repairs. The National Highway Traffic Safety Administration has calculated that, nationwide, the figure comes to $6.5 billion eary year. The estimate includes $1.5 billion for unneeded reparis performed as a result of inadequate diagnosis; $3 billion for faulty repairs where the owner did not get any money back, and $2 billion for unneeded repairs with possible fraudulent intent. IF the total were spread evenly over all 50 states, the $6.5 bill would come to $130 million per state.

Complaints about auto sales and services consistently top the list of grievances received by consumer agencies, according to official records in Northern Virginia agencies.

Fairfax County figures show that auto-related complaints there have jumped in the last nine months by 41 percent over the same period in 1976-77, while the total number of complaints increased by 18 percent. At the same time, auto-related grievances rose 20 percent in the Alexandria office while the total number of complaints went up by only 5 percent. In Arlington auto complaints rose by 17 percent and the total number of complaints remained the same. Figures for the Virginia state branch office are not available.

In February 1978, angry car owners filed nearly 300 complaints with the local offices. Together, the four offices handled an estimated 2,300 auto-related protests in fiscal year 1977. Such cases represent 23 to 30 percent of all complaints the agencies receive.

Consumer officials reports that negligent or deceptive auto repair practices appear to be widespread in Northern Virginia. Fred Albrecht, an investigator who has spent four years with the Virginia Department of Consumer Affairs, said that he still doesn't know where to take his car for repairs. "You can have a bad experience in almost any garage," he laments.

Consumer agencies have a tough time handling auto complaints because complaints are hard to verify, agencies are understaffer, and they do not have highly trained automotive experts to investigate alleged wrongs. The four local officies employ a total of 15 fulltime investigators who must handle a variety of complaints, not just those related to automobiles. The case-load for the four agencies totaled 10,800 last year.

Consumer officials are frustrated because they lack the clout they need to bring cases to a satisfactory conclusion. They cannot compel businesses to redress grievances. Comments Albrecht, "All we can do is mediate and try to get people to do what's reasonable and right. We can't order people to do things." If a firm is uncooperative, agency mediation efforts are useless.

What agencies can do is help prevent a disastrous experience. Car owners who call a consumer office before choosing a repair shop can find out how many complaints have been lodged against a firm, and if the complaints have been settled satisfactorily.

If asked, most consumer offices will also reveal whether a firm will submit to mediation or arbitration proceedings. In addition, some offices will tell callers whether a firm's employes have any special skills or qualifications, if they know about them. However, the offices do not volunteer such information. With the exception of Arlington County, all offices routinely open their case files to the public.

Protections provided by the proposed statutes have turned out to be good business for a nationwide auto association that provides car owners with repair protection for a fee. The American Automobile Association began a successful, consumer-oriented program in the Washington metropolitan area in late 1975, according to William W. Lovell, an association spokesman.

AAA members get much the same services from AAA-inspected garages as would be required by the Waddell bill, amd more. The work in AAA-approved garages is guaranteed for 90 days or 4,000 miles.

Under AAA contract arrangements, the association inspects a garage before it approves it, and then re-inspects it annually to ensure continued compliance with its standards. It withdraws approval if compliance falls below standard. The AAA has the right to investigate and resolve disputes that arise between the approved firm and an AAA member. More than 90 percent of association members are satisfied with the repair protection program, Lovell says.