A verbal direction to proceed at a new "slow pace" on negotiations with the Soviet Union to ban all nuclear tests has been converted into full speed ahead by administration arms controllers, raising new questions about the president's post-Afghanistan sincerity and confusing U.S. allies.

The decision to move along as usual with the Geneva-based comprehensive test-ban talks, recessed Dec. 5 before the Soviet takeover of Afghanistan, is the result of strong pressure from the State Department and the Arms Control and Disarmament Agency. That pressure first diluted, then destroyed the cautious approach advocated by National Security and Pentagon advisers.

The new Strategic Arms Limitation Treaty has been placed on a Senate shelf. The expert of American grain and technology has been sharply limited. sThe United States is thumbing its nose at the summer Olympics in Moscow. So presidential advisers saw no reason to make a business-as-usual exception for the comprehensive nuclear test-ban talks. Hence the "slow pace" verbal order from a National Security Council staffer to the bureaucrats running the test-ban talks.

But that directive did not survive long in the State Department and the ACDA. Bureaucrats there have watched in agony as their favorite projects ("their bread and butter," one official said) have been singed by Carter's reaction to Soviet conduct.

So on Jan. 6 the State Department cabled to its foreign embassies: "We will pursue [the total nuclear test ban treaty] despite the deterioration in U.S.-Soviet relations." That means full speed ahead, with the U.S. negotiating team now ready to leave for Geneva in time to reconvene the talks Feb. 4, the day that had been set at the time of the Christmas recess.

Doubt about Carter's true purpose is compounded when his left hand quietly signals business as usual while his right hand publicly making punishing gestures toward the Kremlin. It is precisely this appearance of contradiction that makes it almost impossible for U.S. allies in Europe and Japan to divine whether the post-Afghanistan Carter is truly a new Carter or just the same old Jimmy wearing election-year hawk's clothing.

Some of the problems with the decision to move ahead with the comprehensive test ban are admittedly endemic. The Joint Chiefs of Staff, for example, have never wanted a complete ban on all testing. They succeeded in reducing the administration's original plan to a three-year treaty, not the five years Carter wanted or, as Moscow wants, a treaty with no time limit.

But the treaty poses other dilemmas for the United States growing directly out of the undisguised Soviet drive to build, flex and uses its military muscles. for one conspicuous example, the United States has persuaded its NATO allies to proceed with a major new weapons program designed to modernize the NATO nuclear force. The total nuclear test ban treaty being negotiated at Geneva would create a nightmare for U.S. scientists and nuclear engineers if weapons testing becomes illegal. The new nuclear warheads to be placed in Western Europe could not be tested. t

By the same token, the president's decision to go ahead with the MX missile, a mobile system calculated to preserve America's land-based intercontinental missiles from Soviet destruction, also will require extensive testing of warheads. Lacking that, warheads will have to be drawn from existing stockpiles.

Indeed an Alice-in-Wonderland mentality pervades the decision to go back to the test-ban table with the Russians at this particular time. If agreement were reached by a sudden twist in Soviet policy that permitted the United States to place seismic verification stations on Soviet soil -- to enforce complience -- the United States would find itself sealed in to an agreement that would deny any way to ensure the reliability of new nuclear weapons. Nor would the United States know for sure, even with on-site inspections, that the Soviets were not cheating.

That became disconcertingly clear when American nuclear scientists were unable positively to identify the source of a strange, nuclear-like explosion that lit the skies in the south Atlantic Ocean Sept. 22. Some nuclear experts are certain the brilliant flash was an atmospheric test explosion; others are not certain. Such uncertainty casts a new cloud over the validity of all test bans -- atmospheric or underground -- and counsels new negotiating caution.

The more compelling need for caution is to prove that Carter's new enlightened look at the Russians is real, not political. On that score, the return to Geneva is a low mark for credibiltiy.