The Justice Department got more ammo in its fight against attorney fees last week when a divided panel of the U.S. Court of Appeals here ordered a drastic cutback in the $3.4 million awarded to attorneys last year in a job bias case against Northwest Airlines.

Judges Malcolm R. Wilkey and Edward A. Tamm ruled that the award, handed down by District Court Judge Aubrey E. Robinson Jr., was too high because Robinson allowed lawyers to use a "prevailing market rate" of up to $175 an hour rather than rates charged by their own firm, reports correspondent Philip Smith.

Attorney Philip A. Lacovara, who represented the airline, said that the decision would reduce the award by $2 million.

The Reagan administration has been pushing for rates of no more than $75 an hour for attorneys who win cases against the government.

Robinson made the original award to the Washington firm of Bredhoff & Kaiser after it succesfully sued the airline for discriminating against 3,300 female employes.

Wilkey and Tamm said they were "aghast" at the amount of time spent on the fee request by Bredhoff & Kaiser and by Arnold & Porter, which received $150,000 for representing Bredhoff in the action.

The appeals judges, who sent the case back to Robinson to refigure the award, disallowed the "risk" bonus commonly given attorneys in such cases, saying "the level of risk was not unusual."

In a sharp dissent, Judge J. Skelly Wright criticized his colleagues for overturning what he called a "carefully reasoned and meticulously documented opinion . . . ," adding that the majority view "injects unnecessary confusion into an area of law I had thought settled long ago."

Wilkey and Tamm accused Wright of "nickel and diming" their fee guidelines.