An Arlington woman filed a $500 million class-action suit yesterday against the Firestone Tire & Rubber Co., claiming that Firestons 500 steelbelted radial tire she and others bought were defective, expensive to replace and threatened their safety.

Cynthia M. Farris, who said that her 1974 Ford LTD came equipped with defective Firestone 500s, claimed in her suit filed in U.S. District Court in Alexandria that Firestone violated several Virginia and federal laws and defrauded more than 100,000 tire purchassers.

Just last week Firestone and the federal government agreed that Firestone will voluntarily recall about 9 million of the tires and the National Highway Traffic Safety Administration will waive any panelties it might have levied against the company.

The NHTSA issued a "preliminary determination" last July that the Firestone 500s had a "safety-related defect" that led to thousands of tire failures.

Under the agreement, Firestone will replace for free every Firestone 500 steel-belted radial made betweet Sept 1, 1975, and May 1, 1976, and still on the road. For those tires produced about six months before Sept 1, 1975. the company said it will provide customers with a 50 percent adjustment rebate on returns.

Farris is seeking compensation for all Firestone 500 purchasers since the tires were introduced in 1972.

Farris is also reqesting recovery of the original purchase, price, new tires, punitive damages of $10,000 per tire purchaser and an injunction requiring Firestone to disclose all facts about the defects of the tires to prospective customers.