PORTLAND — State officials said Tuesday that three of the six oil companies that ship fuel oil to Maine have left the market.

As a result of the cutoff in shipments, the price of industrial-grade No. 6 fuel oil, which is used by utilities and paper companies, has risen by as much as $2 a barrel, according to the state director of energy planning, John Flumerfelt.

Flumerfelt speculated that the cutoff is a boycott resulting from Senate Majority Leader George J. Mitchell’s support for a proposed federal law that would hold oil companies, tanker operators and the owners of spilled oil responsible for the total costs of cleanups.

The bill would not pre-empt laws in states like Maine, which have strict spill-cleanup laws of their own. Maine’s 21-year-old law gives shippers or polluters unlimited liability for cleanups.

“I suspect one of the reasons (for the boycott) was to get to Sen. Mitchell. I think this is a game of chicken,” said Flumerfelt. “But I don’t think anyone can hold us hostage.”

Mitchell told the Central Maine Morning Sentinel that 18 other states already have strict liability laws, so Maine should not be singled out. He added that the federal bill cleared the Senate and House by wide majorities, “so a boycott is unlikely to help.”

A spokesman for Texaco USA said the decision by Texaco Marine Services to stop delivering No. 6 oil to Maine for another company was not related to the congressional legislation but stemmed from corporate concern over spill liability. Because Texaco does not market No. 6 oil in Maine, delivering the product along Maine’s rockbound coast seemed too risky to continue, he said.

Texaco will continue to market gasoline and home heating oil in Maine, said H.G. Ingram, Texaco’s manager of public and government affairs for the Northeast.

Calls to another company that has stopped No. 6 shipments to Maine, Amarada-Hess Corp. in New York, were not returned Tuesday.

Three of Maine’s six industrial oil suppliers have stopped shipping to the state, according to Rob Elder, the state Transportation Department’s director of ports and marine transportation.

“It’s hard to tell how long it’s going to go on or what the long-term impact will be,” said Elder.

Gene Guilford, director of the Maine Oil Dealers Association, said he is puzzled about why the shippers waited until last month to stop delivering. He said the boycott has been applied only to No. 6 oil, apparently because the liability is greatest with that fuel, which is sticky and could coat the coastline if spilled.

Maine industries consume about 10 million barrels a year of heavy oil, which currently sells for $17 a barrel.

Flumerfelt said there is no indication that the boycott will spread to heating-oil shipments.