The new chairman of the Interstate Commerce Commission has declined to vote in a continuing series of truck rate disputes now before the regulatory agency.

Edward J. Philbin, who became ICC chairman last month, said he will not participate in negotiated truck rate cases because of possible conflicts with his earlier voting record as a member of the Federal Maritime Commission.Since 1985, the ICC has faced scores of trucking cases in which a legally filed rate differs from an unfiled rate negotiated between the trucker and shipper.

Typically, the disputes arise when a collection agent for a bankrupt trucker bills the shipper for the difference between a low negotiated rate and a higher filed rate.

Federal law requires the trucking company to charge only the published tariff, but the commission has ruled repeatedly that an unfiled rate negotiated in good faith can take precedence over the filed rate.

Mr. Philbin told reporters at a recent meeting that he faced somewhat similar rate disputes as a member of the FMC.

"But the filed rate doctrine was adhered to right down the line at the FMC," Mr. Philbin said.

The ICC ruled in 1986 that it has the power to make exceptions to the filed rate doctrine if a tariff is found to be unreasonable. No such power resides at the FMC.

Despite the ICC ruling, Mr. Philbin said his strong record of support for filed rates at the maritime commission convinced him to abstain on negotiated rate cases at the ICC.

Mr. Philbin said the ongoing judicial dispute over the legality of negotiated rates - four appellate courts have supported them, one has not - also persuaded him to stay out of these cases.

The Supreme Court has agreed to hear a negotiated rate case, Maislin Industries vs. Primary Steel, on April 16. A decision is expected this summer.

Mr. Philbin's decision not to participate in negotiated truck rate disputes should have no effect on pending cases. The ICC, under former Chairman Heather Gradision, had voted 5-0 in favor of negotiated rates in almost every case.

Mr. Philbin's abstention means future votes likely will be 4-0.

The ICC typically decides one or two negotiated truck disputes a month, although some recent cases have been put on hold pending a Supreme Court decision.

On other issues, Mr. Philbin said the ICC's recent decision to investigate rate-setting practices in the trucking industry was not an attempt at re- regulation.

The commission has been concerned that some trucking companies may be avoiding rate review by simultaneously filing collective and independent rate increases.

The Department of Justice asked the ICC last December to investigate this practice at the Rocky Mountain Motor Tariff Bureau.

The commission deferred the request but is conducting a wider probe of truck pricing activities.

"One has to question if the (rate-making) procedures are being used in a manner not intended by Congress," Mr. Philbin said.

The chairman said truck rate-setting actions, which often include rate increases followed by steep price discounts, have puzzled the commission.

"Frankly, none of us understand it," he said. "We're asking, 'What's going on?' "