The Carter administration came under fire yesterday from the co-sponsor of the Humphrey-Hawkins "full employment" act for placing its new antiinflation effort ahead of job-creation in the President's 1979 economic plan.

Rep. Augustus F. Hawkins (D-Calif.), who was co-author of the measure with the late Sen. Hubert H. Humphrey (D-Minn.), complained at a hearing that Carter's new policies "deviate from the act and go in the opposite direction."

Recalling that the White House had insisted on numerous changes in the bill before Carter finally endorsed the measure, Hawkins told top Carter economist Charles L. Schultze: "You and I better go back to negotiating, I think."

Schultze spent most of his testimony defending the administration's decision to concentrate its efforts on fighting inflation. "Only after we get inflation down," he said, "can we have the political support to spur jobs."

The exchange before the House Education and Labor Subcommittee underscored the widening split between backers of the Humphrey-Hawkins measure -- mainly black groups and old-line liberals -- and mainstream Democratic economists over Carter's new policies.

The Humphrey-Hawkins act, which was passed last year in part as a memorial to Humphrey, calls on the administration to trim the jobless rate to 4 percent by 1983 and slow inflation to 3 percent -- two sharply conflicting goals.

Most economists warned previously it would be unrealistic to hope to meet the measure's unemployment target without seriously exacerbating inflation. Analysts say the addition of the anti-inflation goal made the job almost impossible.

The clash came as, separately, former Johnson administration economic adviser Arthur M. Okun warned the oil cutoff by Iran would worsen prospects for the U.S. economy, but said immediate decontrol of oil prices would be "disruptive."

At a breakfast meeting with reporters, Okun said it now was "more likely than not" that the economy would fall into a recession. He also cautioned the economy was still "stubbornly strong" and "going too fast" to help slow inflation.

Okun also criticized proposals for a new "value-added tax" -- a form of national sales tax, now widely used in Europe.