Twin-trailer trucks will have more freedom to travel smaller roads to reach freight terminals and fuel stops under new federal rules announced Thursday.

The Department of Transportation ended a seven-year fight between the federal government and some states by issuing national regulations that let long truck combinations travel well beyond major highways.A handful of mostly Eastern states that had sharply restricted truck travel beyond major roads will be forced to allow wider access unless they can prove a serious highway safety threat.

"These states will be brought into line with the (prevailing) system, which provides for liberalized access," said Kevin Heanue, director of the Office of Planning at DOT's Federal Highway Administration.

Truckers have complained for years that a small group of states have prevented them from using access roads that lead to freight terminals, where loads are picked up and delivered.

More than 40 states allow twin-trailers and other longer rigs to travel on all, or most, access routes. The new DOT policy will have little effect on them. The regulation is likely to draw protests from the remaining states.

"There will be people in many states in the Northeast who will find it difficult to accept this rule," Thomas Larson, federal highway administrator, said in an interview. "But it's clear by now that it's time to take a national perspective (on this issue.)"

The new rule applies to a group of longer rigs approved for national use in 1982. They include a tractor pulling a single, 48-foot long trailer, twin 28-foot trailer combinations and any tractor-trailer that measures 102 inches wide.

The original federal legislation allowed those longer and wider rigs to travel on a designated system of about 180,000 miles of major highways. Access to terminals and to food, fuel and repair facilities beyond these highways was left to each state's discretion, although the law generally required ''reasonable" access.

Eight states - including Pennsylvania, Massachusetts, Connecticut and Georgia - imposed access rules that many truckers, shippers and federal officials considered unreasonable.

The new rule, a victory for the trucking industry, resolves the dispute by

broadly defining "terminal" as "any location where freight originates, terminates or is handled in the transportation process, or where carriers maintain operating facilities."

The regulation says states "may deny access to terminals . . . only on the basis of a safety and engineering analysis of the access route."

Moreover, each state that restricts access for longer trucks must submit its access policies to the federal government for review within six months.

These access policies would describe how the states handle requests from truckers to open additional routes for longer rigs. If the state rules do not provide wide access, its regulations are pre-empted by the federal regulations.

Transportation Department officials said the new rule does not supersede existing state truck bans on residential streets, weight-posted bridges or on routes that cannot safely accommodate these larger trucks, including narrow- lane roads.

Robert Farris, vice president of policy at American Trucking Associations, said truckers generally were pleased with the new rule.

"Our principal concern was with states that wanted to ban truck access for illegitimate reasons, then hide behind a safety cloud," he said.

The new DOT rule is based largely on recommendations by the Transportation Research Board, a quasi-governmental organization that issued a 1989 report endorsing wider access.

The access rules drew a sharp protest from Gerald Donaldson of the Center for Auto Safety, who said twin-trailers are not safe on smaller roads.