The half-page ad in the Northern Virginia Yellow Pages touted "expert technical advice," but those dialing a number listed for National Tire Wholesale Inc. in Fairfax were probably startled to find such high-caliber guidance on the other end of the line.

Instead of tires, brakes and struts, what they got were torts, wills and deeds, the law firm of Doherty, Sheridan & Grimaldi.

"We would average 20 to 30 tire calls," groused lawyer Dana L. Scott. "And that was in the morning. Sometimes we got 10 or 20 in the afternoon."

Angered, Doherty, Sheridan & Grimaldi did what comes naturally for lawyers. They sued.

The lawsuit, filed in Fairfax Circuit Court last week, seeks $35,000 in damages from the Chesapeake & Potomac Telephone Co. of Virginia and the Reuben H. Donnelly Corp., which produces the Yellow Pages for the phone company.

The law firm's number -- 698-7700 -- was listed in the 1984 Yellow Pages as the number for NTW's Fairfax showroom. That was, Scott said yesterday, "probably a typo," since it missed the correct number -- 698-7770 -- by one digit.

As a result of the error, the law firm has had "to suffer increased costs and expenses," including the hiring of additional staff members, according to the suit.

Scott said the firm, located on Arlington Boulevard, hired a full-time receptionist because of the tiresome tire calls.

Law firm employes "have been caused to suffer, continue to suffer and will in the future be caused to suffer lost time from work and loss of business," the lawsuit alleged.

Even though the problem was corrected in the 1985 Yellow Pages, the firm is still getting the calls, Scott said.

Harry N. Doyle, a C&P spokesman in Fairfax, said yesterday that the company had not been served with the suit and therefore could not comment on it.

"When we make a typo we unfortunately have to live with it for a year," Doyle said. "If it happens once it's too often," he said. "We're real proud of our batting average."

A spokesman for the Reuben H. Donnelly Corp. said he had not seen the suit, either, and could not comment.

"Oh boy," said Ray Butler, the assistant manager of NTW's Fairfax showroom, when asked yesterday about the number of calls the store gets on a typical day. "We get quite a few."

Butler said that depending on whether the company is having a sale, the store, at 2995 Prosperity Ave., gets about 200 calls a day.

Don Horan, a salesman at the store, said some customers would say: "You know your phone number is listed wrong in the phone book."