The Interstate Commerce Commission, in a ruling that shocked the oil industry, yesterday rejected as unjust and reasonable - and too high - the transport rates proposed by owners of the Alaska pipeline.

In a unanimous decision, the commission told the eight oil companies - which have spent $9.2 billion and eight years building the 800-miles - to reduce their asking prices by 20 per cent and refile for approval.

The oil companies - Exxon, Standard Oil of Ohio, Atlantic Richfield, British Petroleum, Union Alaska, Mobil Alaska, Amerada Hess andom $6.04 to 6.44 per barrel, depending on each firm's financing. The ICC said it would accept rates no higher tha $4.68 to $5.10.

The reductions will have little effect on the price of oil in the lower 48 states. That price is fixed by the Federal Administration and is geared to the worldwide competitive rate of $14.50 per barrel.

But the ICC's ruling will mean upwards of $150 million more in tax and royalty revenues of Alaska, a large percentage of which has been budgeted for more schools, roads, hospitals and fishries for the Eskimos.

A. Daniel O'Neal, ICC chairman, said commission members were influenced by the detrimental impact high tariffs would have on Alaskans. He indicated that the deciding factor, though, was a deep-seated disagreement over how the rate of return on the project should be calculated - specifically, whether interest payable on the debt used to finance the pipeline should be counted as an expense. The commission said it should not.

Last month, the agency ordered an investigation into the complexities of pipeline rate-setting, so that whatever rates are adopted now will only be interm prices.

Sohio President Joseph Harnett said last night he was "astonished" by the ICC's decision, and Allen Murray, president of Mobil Oil, said he was "shocked." Other oil corporation chiefs predicted that the ruling would have a chilling effect on future business projects subject to government regulation.

The oil companies are expected to appeal the decision in federal court, challenging the power of the ICC to suspend initial rate filings. Spokesmen for the firms yesterday left open the possibility that the pipeline might be shut down pending an outcome to the dispute.

Oil began flowing last week from the Prudhoe Bay Field on the Nortt Slope. The crude is not expected to reach Valdez on Alaska's south coast until mid-July, giving the companies some time in which to act.

"We do have time to take a look at this decision and that's we're going to do," said Ricahrd Flynn, a lawyer for Exxon.

Hoping to avoid an outright rejection by the ICC, the oil companies had offered to refund to shippers and the state any revenues a subsequent investigation found to be excessive.

But lawyer for the state and the Eskimos argued that the possibility of refunds was inadequate protection, and the commission agreed.

The ICC also sided with the Justice department, which had opposed the original tariffs on the ground they were too high and would discourage further competitive exploration of Alaska oil reserves.