Confusion over President Carter's trade policy toward Moscow climaxed on Aug. 10 when National Security Adviser Zbigniew Brzezinski read a headline in The Washington Post that the celebrated Dresser sale of oil-drilling technology to the Soviets had been approved by Commerce Secretary Juanita Kreps.

With Secretary of State Cyrus Vance listening in on an extension. Brzezinski made an urgent phone call to Kreps to ask: Is it "too late" to reverse this?

"No," replied the secretary of commerce.

Commerce Department officials, who had pushed hard inside the government for approval of the $140-million drill-bit plant for the Russians, held their breath - waiting for the new order clearly suggested by Brzezinski's question. It never came.

That incident captures the ambivalence at highest administration levels on whether and how much to use U.S. technology as a political weapon to moderate Soviet violations of human-rights commitments, harassment of American businessmen in Moscow and other political wrongs. Having marched up the hill last month flying the banner of trade reprisals against the Kremlin, Uncle Sam was now marching back down with approval of the drill-bit plant (to be built by Dresser Industries of Dallas).

Hence, the familiar questions: What is Jimmy Carter really up to? What does he want?

Once again, the president has raised a specific expectation by policy pronouncements pointing in one direction - then, without preparation or explanation, going in the other. He retains his new power to veto energy-rated technology sales to Moscow. But judging from the Dresser case, the Kremlin can be excused for not panicking.

On Brzezinski's desk when he read that headline was a sharply pointed letter to Carter from Sen. Henry M. Jackson (D-Wash.) in his capacity as chairman of the permanent investigations subcommittee. "Given your new policy of controlling energy-related technology," Jackson wrote on Aug. 7, "it would be ironic if the largest such transfer in recent years were the first to be consummated under your new policy guidelines."

Delivered three days before the Commerce Department leaked its final approval of export licenses for the Dresser drill-bit plant, Jackson's letter flashed a political danger sign. Jackson revealed just how far he wants to go to block the Dresser shipment: a full-scale investigation of its military and political implications at a time of heightened U.S. - Soviet tensions.

Jackson's subcommittee staff is now digging into economic facts that may well refute this contention by Kreps: If the Russians were denied the Dresser plant, they could buy everything connected with it - including such high technology as electronic beam welders - in Wester Europe, Japan or even Eastern Europe.

So Jackson's letter was a polite request for the president to postpone final approval on the Dresser plant "while the subcommittee is inquiring into" national security matters raised by the sale. The only answer to his letter was the Post headline disclosing that the Commerce Department had preempted him. Far from backing down, Jackson still intends to put pressure on the administration by pushing his investigation.

He has powerful allies, one of whom is Energy Secretary James Schlesinger. Schlesinger's office notified Rauer Myer, director of export control in Commerce, by letter on Aug. 4 that Schlesinger strongly opposed an export license for the electronic beam welder.

Oddly, this went unmentioned when the Commerce Department informed Brzezinski that every agency involved in the matter - with te technical exception of the State Department - had approved the sale.

The reservation of State, strictly temporary, was tied to Soviet treatment of Francis Jay Crawford, the American businessman hauled from his car and arrested on trumped-up currency-violation charges. The Crawford outrage delayed the State Department only until Aug. 8. Immediately thereafter, Commerce formally approved the package.

An angry Schlesinger was no informed about the final Commerce Department decision until he read it in the paper. His Energy Department normally is not involved in export-control policy, but the president had made Schlesinger an adviser on the Dresser plant because of his background as former director of central intelligence and secretary of defense.

How far Schlesinger will now go to block the license for the electronic beam welder is uncertain, but he is concerned that piece of technology has military value. Beyond that, Schlesinger agrees with Jackson that approval of the Dresser plant makes a farce of the administration's new "policy" of restraining sale of energy-related technology to the Soviet Union.

It also raises this question: What signal did Carter really mean to send the Russians when he got "tough" last month?