LOS ANGELES, JUNE 29 -- Atlantic Richfield Co. said today that it had paid $800 million to the Internal Revenue Service to settle a dispute over windfall profit taxes on Alaska oil.

The payment settles a claim for back taxes and interest that totaled $1.8 billion, believed to be the largest claim ever presented to a company by the IRS. In settling the dispute, Arco admitted no wrongdoing.

Arco said the payment will resolve all IRS claims for additional windfall profit taxes on its North Slope production from 1980 to 1985.

Arco had set aside reserves since the mid-1980s to cover settlements of disputes over Alaska oil. It said the reserves covered the payment. ''So the settlement payment will have no impact on earnings,'' said spokesman Al Greenstein.

The IRS started investigating Arco in the mid-1980s after rival oil companies complained that the company's internal pricing policies were unjustifiably minimizing its taxes, allowing it to charge less for gasoline than rivals in California. Arco denied the allegations.

The dispute centered on the value assigned by Arco to crude oil it pumped from North Slope wells. The IRS contends Arco assigned the oil a value lower than it should have at that point, lessening the windfall profits tax, which is based on a benchmark price derived from past production.