With just three weeks left before the District of Columbia's mandatory insurance law takes effect, thousands of local motorists are still uninsured, insurance officials said yesterday.

Only 150,000 of the 250,000 car owners in the District now carry auto liability coverage. The other 100,000 are driving without insurance, because it is either too difficult for them to acquire or because it costs more than they can afford to pay.

For a rundown on automobile insurance requirements in the District, Maryland and Virginia, see the Consumer Update column in today's Weekly sections.

Interviews this week with officials of major insurance companies suggest that uninsured drivers now seeking to purchase insurance to comply with the new law will have a hard time getting bargain rates.

"People rushing in the door on Oct. 1 (or before) are going to have to pay higher prices for car insurance--there's no use gilding the lily on that one," said Edward J. Harvey, public affairs manager for Allstate Insurance Co.

It's not the lack of previous insurance that will affect their rates, he said, but the fact that many drivers have been uninsured precisely because they didn't qualify for low insurance rates in any case--because of lack of driving experience, the condition or age of their cars or their driving records.

Such applicants traditionally are surcharged according to the number and type of accidents and moving violations on their driving records. In some cases, new applicants who don't meet the criteria for the low-risk policy rate are referred to another plan or company that will accept high risk drivers--but at sharply higher rates.

The difference in cost for a driver with a preferred policy rather than a high-risk policy is dramatic. One recent study by the D.C. Department of Consumer and Regulatory Affairs found that minimum insurance required by the new District law for a 40-year-old male could range from a low of $174 to a high of $370, assuming the man has no chargeable accidents or violations, drives seven miles one way to work and 10,000 miles a year in a car that isn't a sports or high-performance model.

The low price of $174 was the rate for State Farm Mutual, which won't accept any new policyholder with an accident or traffic conviction within the past three years. The high price of $370 was the rate for the D.C. Automobile Insurance Plan, which was established by the District to provide insurance for motorists who can't get regular insurance.

District law forbids a company from refusing to sell insurance to an applicant solely because he hasn't been insured in the past, said Phyllis Blair of the D.C. Department of Consumer and Regulatory Affairs. "However, if you have never driven and you lack experience and a driver's record that can be reviewed by the company, you can be refused for that," she said. A driver also can be turned down when he doesn't meet fundamental requirements set by the company for all new applicants, she said.

Each company has its own rules for deciding which applicants are acceptable and which are not.

Here is a summary of the guidelines for some major companies, based on information provided by the companies:

Geico (Government Employees Insurance Co.) considers driving records, driving experience and the type of automobile being insured, said regional vice president Edward H. Utley.

"Underwriting is a matter of judgment, so we have no firm guidelines," he said. "We look at the accidents and convictions to see what types they are--a 60 mph speeding ticket on a freeway wouldn't be as bad as a 50 mph speeding ticket in a residential section."

New applicants should have at least three years' experience, however, so that Geico can assess their record. "No accidents and no convictions doesn't mean much if you have driven only one day," he said.

Certain cars also are less desirable to Geico officials than others. "We are very concerned about high-powered cars, such as the 280Z with the turbo engine, and the kind of accidents they are involved in," Utley said. "And we're not wild about vans with murals painted on the side, because if they are in an accident, they are hard to fix to the owner's satisfaction."

State Farm agents can issue two kinds of policies--the low-priced preferred policy from State Farm Mutual and the more expensive high-risk policy from State Farm Fire & Casualty Co., said company spokesman Robert Sasser.

To qualify for the State Farm Mutual policy, a new applicant over the age of 25 must be free of accidents and convictions for the past 36 months. If the applicant has had one conviction or one accident, he may qualify for the State Farm Fire & Casualty policy, which generally costs 50 to 60 percent more than the State Farm Mutual rate.

Those drivers who have had more than one accident or conviction during the past 36 months aren't eligible for either State Farm policy and will be referred elsewhere, perhaps to the D.C. Automobile Insurance Plan.

Acceptance rules at State Farm for those under 25 are more rigorous, but any new applicant turned down by the agent can ask for a review by the company's underwriters. That review could take several weeks, however.

Allstate Insurance Co. generally requires that a new applicant buying a single-car policy have no moving violations or at-fault accidents for the past three years. For a multicar policy, Allstate will allow one moving violation within the past three years.

The company typically tries to avoid insuring luxury cars, such as the Maserati or the Ferrari, because Allstate rates weren't designed to accommodate such expensive models. High-performance cars are unpopular because "people tend to drive fast in high-performance cars and that makes them a greater risk," Harvey said.

Liberty Mutual Fire Insurance Co. weighs the driving record, length of driving time, ability to pay premiums and type of vehicle, said spokesman Alex Caswell.

"We would prefer a clean driving record for three years, but an applicant could have one ticket or accident and, if everything else is all right, still qualify," Caswell said. "And we would look for someone who had been licensed at least a year."

He said that the company also checks to see if the applicant has a record of steady employment to determine if the person can pay for the insurance.

Aetna Life and Casualty Co. considers driving records and vehicle age and condition, said regional general manager Hylan T. Hubbard.

To qualify for a preferred policy, the applicant must be free of convictions and accidents for three years. A more expensive standard policy is available to applicants with no more than one or two convictions or accidents.

Hubbard said that Aetna may refuse to insure cars that are too old--"10 years or so"--or "are in really bad shape and condition."