The National Highway Transportation Safety Administration wants to scrap a federal program that requires tire manufacturers to test their products and assign them ratings as a guide to consumers.

Fighting a somewhat lonely battle against the change is the Uniroyal Tire Co., which has parted ways with its competitors and the tire manufacturers' trade group in supporting the program. Not surprisingly, the firm is the only major manufacturer to use the tire ratings when it markets its tires.

"The consumer needs an objective yardstick to measure the conflicting quality claims of the tire manufacturers," Robert H. Horning, vice president for marketing of Uniroyal, said during hearings on the program this summer. "A uniform standard for tread-wear rating helps by giving people a basis for comparison."

Under the program, manufacturers of all passenger car tires sold in the United States must test their tires according to government-prescribed procedures and assign them ratings, or grades, designed to reflect the performance of the tire tread. NHTSA then runs checks to make sure the tires meet the assigned grades. The rating, along with traction and temperature resistance data, is designed to help the buyer make a decision when he needs to replace his tires.

The tread-wear grades are supposed to indicate how many miles a tire can be expected to last. The grades are designated by number, generally running from 70 through 240. According to the government, a tire graded 150 should give the customer 50 percent more mileage than one graded 100. On the government's test course, it says, a tire with a 100 tread-wear grade will last for about 30,000 miles, with some variation depending on the way a person drives and where, and whether the tires are inflated properly.

This summer, however, NHTSA proposed suspending the grading requirements because of what it termed "serious concern over accuracy of the tread-wear information."

Raymond A. Peck Jr., the agency's administrator, said that his proposal was based on agency and industry tests that produced different results for the same tires. "We began to have questions about whether the test results are sufficiently reliable and repeatable," he said.

Peck said that in some of the agency's tests, the rank order of some of the tires tested changed. For instance, a tire that finished last in one test, finished first another time. "We don't know whether the fault is in the testing program, or whether in the real world, or whether it's just not possible to determine tread wear accurately," Peck said.

"We are not faced with whether a government-sanctioned program is providing sufficient information or perfect information . . . ," he said. "The question we have is whether a government-sanctioned program is providing misleading information."

But Uniroyal officials disagree strongly. Although they admit the testing system is not perfect, they contend it is "reliable, workable and not misleading."

"What is wrong with it can be remedied by running changes in the present system, without sacrifice of its present utility," said Robert H. Snyder, the company's vice president of tire technology.

Clarence M. Ditlow III, director of the Center for Auto Safety, a consumer advocacy group, agreed. At last summer's hearing, he said, "As has been the problem in the past, NHTSA is once again bound up by the paralysis of perfection in its search for a completely accurate tread-wear test. To the extent that there are errors in the test procedures, NHTSA should . . . move to correct the errors . . . rather than throw out the single most wanted piece of consumer information on tires."

Snyder admitted that differences in grading practices among manufacturers, coupled with some variability inherent in the test procedure, can produce widely different ratings for tires of nearly the same grade. But those differences could be reduced, he said, if NHTSA would adopt a uniform procedure for manufacturers to follow when they assign grades. He also argued that the agency's testing problems were associated with the tester, not the test itself.

But even now, Snyder said, a conventional statistical analysis of the gradings indicates that they are of genuine value to a purchaser. Generally, there is a correlation between the test grade and the assigned grades, he said.

Uniroyal is the only major tire company to have used the grades, in comparison with its competitors', as a marketing tool. Snyder said the firm found that the system works "quite well" for their tires and permits an accurate rank ordering of the various brands the company manufactures.

But all of the 11 other major domestic tire manufacturing members of the Rubber Manufacturers Association oppose the program.

Although the tire grading system was mandated by Congress in 1966, the program didn't go into effect until 1979. In the interim were years of litigation, with consumer groups suing successfully to get NHTSA to issue the standards and the tire companies -- including Uniroyal in the past -- suing to get them blocked.

While Uniroyal decided to stop fighting the regulation, the other companies didn't quit. In his testimony at the NHTSA hearing, Robert W. Milk, a vice president of the Goodyear Tire & Rubber Co., noted that the companies had made many of the same arguments to the agency and the courts previously. "The tread-wear test procedure does not generate repeatable results," he said. "There are too many uncontrollable variables in that procedure, including drivers, environment and vehicles . . . ."

NHTSA, which is studying the hearing record, estimates that the tire manufacturers spend about $10 million a year to test for tread-wear grade. With about 130 million tires sold in the replacement market every year, the consumer's cost for the tread-wear system works out to less than 8 cents a tire, Uniroyal's Horning said.