WASHINGTON — After an eight-year struggle, Sen. George J. Mitchell and other members of Maine’s congressional delegation prevailed over oil company lobbyists who sought to abrogate the state’s first-in-the-nation oil spill cleanup law.

As a result, Maine and 18 other states that adopted legislation modeled after Maine’s 1970 statute may continue to sue oil companies for the full costs of major spills like the $2 billion disaster caused by the Exxon Valdez in Alaska’s Prince William Sound two years ago.

Industry lobbyists, backed by the Bush administration, had sought to win enactment of a United Nations-sponsored accord that would have capped the liability of tanker companies to only a fraction of actual cleanup costs.

One immediate consequence, industry officials warned, was that the major oil companies will stop shipping oil to states like Maine with unlimited liability statutes because no insurance company would extend coverage to their tankers who sail into such waters.

Addressing the Senate, Mitchell said, “The 11 million-gallon Exxon Valdez tanker spill and other spills in New York Harbor, California and Texas amply demonstrate that all parts of the country are at risk. A national response is needed to this problem.”

Sen. William S. Cohen, who co-sponsored Mitchell’s bill to protect the local unlimited liability cleanup statutes, said, “Had Alaska not had (a cleanup law modeled after Maine’s) and been able to respond quickly to the Valdez spill, environmental damages would have been much worse.”

“This is a good bill for my state of Maine and for any state that has its own oil spill cleanup fund and liability laws,” Cohen said.

Approved by a 99-0 vote, the Senate bill adopts measures worked out last month by a House-Senate conference committee. The House is expected to vote on the bill Friday.

Without some limit on oil-spill liability, industry officials said that oil companies will sell their tankers to fly-by-night, single-ship corporations. Since the entire assets of such companies would be just one tanker, there would no way to recover money for a cleanup. The corporation would scrap the ship and go bankrupt.

Maine’s $6 million cleanup fund, the current balance of which is $3 million, would be far too small to cope with a spill on the magnitude of Prince William Sound. It has worked well in the handling of smaller spills, however, according to state officials.

The Maine fund is replenished by a 3-cents-per-gallon tax on oil products delivered to the state.

The grounding of the Tamano tanker in 1972 in Casco Bay was Maine’s largest spill, totaling only 100,000 gallons. By comparison, the grounding of the Exxon Valdez dumped 11 million gallons of fuel in the waters off Alaska.

The Maine Legislature recently created a commission to review the state’s 20-year-old oil spill law and to recommend changes.