The National Highway Traffic Safety Administration has warned General Motors Corp. that it could be in violation of federal law if it does not conduct a full-fledged safety recall for spare tire problems with its new X-body cars.

In an exchange of letters with GM engineering officials last week, NHTSA enforcement official Lynn Bradford raised "serious questions" over GM's handling of "wheel interference" problems involving the new compact-size spare tires.

In an April 6 letter to Ralph Morrison, director of GM's product investigation, obtained by The Washington Post, Bradford wrote: "We have received information that General Motors has sent representatives to GM dealerships to explain to dealers how to fix several items on Citation vehicles which fall into the area of safety defects.

"We are told," the letter continues, "this is being done in this manner to eliminate the need for paper work and the requirement to notify the National Highway Traffic Safety Administration."

The letter then cited two particular defects in question, "wheel interference" and "wiring harness problems," and asked GM to reply within five days.

GMhs response, also obtained by The Post, denied the allegations.

The letter from Morrison alleged that the GM officials were calling on their dealerships "in order to expedite all repairs prior to our new car announcement."

"There was certaintly no attempt to circumvent the law as implied in your letter," Morrison wrote.

Bradford responded to GM's answer with an angry letter on April 17. "Apparently," Bradford wrote, "you did not carefully read my letter of April 6. In it I specifically cited a 'wheel interference' problem involving the spare wheel on these vehicles. Your response of April 12 does not address that subject."

The problem involves evidence that the new small-sized spare tires, when placed on the front wheel of the new front-wheel drive compacts, may come in "contact with the brake caliper."