Prices for the no-fault automobile insurance that District residents must have by Oct. 1 will vary widely, with some companies charging more than twice as much as others for identical coverage, according to a comparison of rates released yesterday by the D.C. Insurance Administration.

Depending on the company, minimum no-fault coverage will be available for some policyholders, for example, for as little as $385 a year or as much as $961, the comparison shows.

"This rate information is brand new. It may come as a surprise even to some of the companies who know what their rates are but don't know what other companies are charging," said James Montgomery, an official in the Insurance Administration, part of the Department of Consumer and Regulatory Affairs.

Companies set their rates based on experience, operating costs and mix of policyholders they insure. Some companies, such as State Farm Mutual Insurance, which traditionally accept low-risk drivers, tend to have lower rates than other companies that insure high-risk drivers.

The rates on which the comparison is based were approved by the Insurance Administration after a review aimed at making sure they will be "fair to consumers and insurance firms," said Margurite C. Stokes, Acting D.C. Insurance Superintendent. The review, by the Insurance Administration and the People's Counsel, which represents consumers in utility rate cases, included a series of public hearings, Stokes said.

D.C. residents who have automobile insurance can expect their companies to convert their coverage to include the new no-fault insurance and to bill them accordingly. Resident motorists who don't have automobile insurance will have to contact a company or agent to purchase the mandatory coverage.

The rates comparison shows the amounts that six different categories of drivers would pay for minimum no-fault coverage from major insurance companies. These are examples of three driver categories and the rates they would pay:

A 40-year-old married male driving seven miles one way to work in a conventional automobile (not a sports or high-performance car) and no more than 10,000 miles a year altogether, with an occasional 16-year-old male driver who has had one chargeable accident and without a driver-training discount. Annual rates for minimum no-fault would range from $385 from Allstate Insurance Co. to $961 from Criterion Insurance Co.

Other rates noted between those two extremes are: State Farm Mutual, $406; Liberty Mutual Fire, $452; Nationwide Mutual, $486.40; Geico (Government Employees Insurance Co.), $510.30; Aetna Casualty and Surety, $554; Dairyland Insurance Co., $588; Insurance Services Office (which represents about 160 insurance companies), $596; and Colonial Penn Insurance, $777.20.

A 22-year-old single male principal driver who drives seven miles one way to work in a conventional automobile and 10,000 miles a year with one chargeable accident. The lowest rate noted is $335 from Allstate and highest is $688.50 from Colonial Penn.

A 66-year-old male who drives seven miles one way to work, has no youthful driver in the household, no chargeable accidents or violations and no sports or high-performance car. The lowest rate in the comparison is $174.28 from State Farm Mutual and the highest is $300 from Dairyland Insurance.

The minimum no-fault package on which the rate comparison is based includes personal injury protection for the policyholder and passengers of up to $100,000 medical and rehabilitation benefits, up to $24,000 for work losses and up to $2,000 for funeral expenses; bodily injury liability for accidents caused by the policyholder outside the District, with benefits of up to $10,000 for one injured person and up to $20,000 for two or more injured persons; property damage liability, which pays up to $5,000 for damage to another person's property for accidents that occur in or out of the city; and uninsured motorst coverage, which protects the policyholder against drivers who aren't insured, of up to $10,000 for bodily injury liability for one person, up to $20,000 for bodily injury liability for two or more persons and up to $5,000 for property damage liability.

The insurance department is publishing a brochure, which should be available Aug. 1, containing the rate comparison and an explanation of the no-fault law. It has also established a consumer hotline -- 347-4100 or 727-2426 -- to answer questions about the no-fault law.