BALTIMORE, DEC. 30 -- Radar detector enthusiasts battled Geico Corp. today in an attempt to stop the insurance giant from denying them car coverage because they own the popular electronic dashboard devices.

Geico, believed by insurance industry specialists to be the only insurer in Maryland with such a policy, has refused to cover motorists who use radar detectors, contending that those drivers cause a disproportionately large number of accidents on Maryland highways and therefore pose high risks for insurers, an argument that detector supporters reject.

"There is only one reason for using a radar detector: to allow the user to exceed the speed limit without being caught . . . and that increases the likelihood of accident involvement," said James D. Hospital Jr., risk research director at Geico, one of Maryland's largest car insurers.

Not so, countered Jim Baxter, president of the Citizens Coalition for Rational Traffic Laws. In fact, the opposite is true, he said, with studies showing that motorists "who typically travel 5 to 10 miles an hour above the average speed for a given highway represent the safest pace group on that highway."

The clash came before Assistant Maryland Insurance Commissioner Thomas Raimondi, who was asked by Baxter's group and a national radar detector manufacturer's lobby to order Geico to stop its practice of automatically refusing to insure drivers who own detectors.

Geico, which insures 220,000 vehicles in Maryland, said it does not know how many drivers have been refused insurance because they owned detectors. Under Geico practice, drivers are asked if they own a detector when they apply for insurance or seek to renew a policy.

Raimondi is expected to rule on the issue in late January or February. A ruling against Geico could have national ramifications, observers said, since the giant company insures vehicles in many states and has applied its no-detector rule nationwide.

About 80,000 radar detectors are being used in Maryland and 4 million throughout the United States. The detectors, small dashboard-mounted sensors costing from $70 to $300, are legal in Maryland. Attempts to outlaw them by the legislature have failed repeatedly in the last dozen years. They are illegal only in Virginia, D.C. and Connecticut.

Today's hearing pitted Geico officials against not only Baxter but also automobile writer John Tomerlin, highway affairs analyst for the 700,000 circulation Road & Track magazine, and Annapolis lobbyist Bruce C. Bereano, who appeared on behalf of RADAR, an Ohio-based trade association representing manufacturers in the $400-million-a-year radar detector industry.

Armed with separate and contradictory statistics, each side claimed the truth.

Geico officials cited a Maryland State Police study showing that while only 3 percent of cars are equipped with radar detectors, 33 percent of the speeders ticketed in Maryland from July 1985 through May 1986 had detectors. Related insurance industry studies show, they said, that drivers with a record of speeding generally are more likely to be involved in road accidents than drivers with no record.

Bereano retorted that an independent study by the Yankelovich Clancy Shulman survey organization in 1987 showed that radar detector users "drive at least as safely" as motorists without detectors. Detector users, he said, are driving enthusiasts who, while they may exceed speed limits like many other people, are especially alert and "aware of their surroundings."

Tomerlin, along with Baxter, said other studies show that the lowest accident rate occurs among cars going at the average speed and 5 to 10 mph above the average speed on a given roadway. The "average" speed, they noted, often is somehat above the posted limit as well.

Tomerlin said accident rates are higher both above and below the "average speed" segment of the traffic, "but the most dangerous accidents occur at the slower speeds."

Raimondi expressed concern that the studies offered by Geico may not meet standards of recent Maryland court rulings requiring specific statistical evidence to justify refusal to insure a driver or group of drivers.

While the Geico studies show a correlation between speeding and accidents, users of radar detectors are not directly tied in, he said.

Geico attorney Gary Gertz said radar detector users "mask their true driving record" by slowing down when their detectors alert them to police on the road.