Motorists in Philadelphia, New York, Miami and Boston pay the nation's highest auto insurance rates, in part because they file at least 50 percent more personal injury claims than other drivers in their respective states, an industry study says.

The report by the Insurance Services Office Inc. and the National Association of Independent Insurers said motorists in Seattle, San Diego and Nashville, Tenn., paid lower rates because they filed fewer claims compared to their state averages.The study ranked 18 of the 26 largest cities in the country as "high cost," "low cost" and "neutral" based on accident frequency, claim frequency, theft rate and other factors compared to the rest of their respective states.

The survey did not compare the cities to each other.

"Eighteen large cities in 13 states were selected in an attempt to identify characteristics affecting high insurance costs," said Diana Lee, spokeswoman for the National Association of Independent Insurers.

"Rather than make a direct comparison of the experience among cities themselves - which are subject to variations in state laws and regulations - the experience of these cities is compared to the average of the states in which these cities are located," she said.

The cities listed in the survey as high cost when compared to their statewide averages included Baltimore, Boston, Chicago, Cleveland, Detroit, Los Angeles, Miami, Newark, N.J., New York and Philadelphia.

Low-cost cities listed in the survey included San Diego; Seattle; Columbus, Ohio; Jacksonville, Fla.; Nashville, Tenn.; San Jose, Calif. San Francisco and Milwaukee were classified as "neutral" cities.

Jacksonville, San Diego and San Jose reported claim frequencies more than 20 percent lower than their state averages, the study said.

Among the high cost cities, Philadelphia led the nation in frequency of bodily injury claims relative to its state averages.

Insurance companies reported losses of $122.1 million in personal injury claims in Philadelphia within the five years between 1981 and 1986, the most personal injury claims of any of the 18 cities studied and three times more claims than the rest of Pennsylvania.

"For the same kind of automobile accident case where there are no claims . . . throughout the rest of the state, you can count on it in Philadelphia," said Henry Hager, president of the Insurance Federation of Pennsylvania.

"There's no question about the fact that they sue more often in Philadelphia than anywhere else in the state. It holds true with other cities, but not to the extent of Philadelphia."

Philadelphia ranked highest in three other categories, including loss cost, claim severity of property damages and frequency of uninsured motorist claims.

Newark finished second in personal injury claims with $55.7 million in personal injury claims in the five-year period, followed by Baltimore, Los Angeles and Miami.

Newark topped the list for the frequency of property damage liability relative to state averages, with total losses of $32.5 million in the last five years.

Boston reported the highest frequency of comprehensive injury claims, with 213.2 claims for every 1,000 autos within the last five years. Boston was followed by Newark, N.J., New York, Philadelphia and Detroit.