Concern about the competency of U.S. negotiators on SALT is raised by this remarkable fact: The new U.S. proposal put forth in Geneva sets a "ceiling" on production of the Soviet Back fire bomber at a far higher level than the Russians can possible achieve.

The failure by Secretary of State Cyrus Vance to reveal the proposed "Celing" to a Senate subcommittee May 26 might indicate self-doubt by U.S. policymakers about its worth. But defense-oriented members of Congress suspect duplicity less than incompetency. As details of Vance's session in Geneva with Soviet Foreign Minister Andrei Gromyko have become known, doubt has grown whether the United States knows what it is going in the arms-control talks.

It is debatable just how much of a retreat is represented by the proposal submitted at Geneva and rejected by Gromyko. If the Russians finally accept top-secret details as described to the senators by Vance (which is dubious), the treaty surely would be ratified by the Senate. What is worrisome for the long haul are deficiencies in both grand strategy and petty details.

The heart of the concern is the fact that just one month after President Carter's bold, tough but still reasonable SALT package was tabled in Moscow, concessions were offered in Geneva. The inescapable conclusion is that, contrary to Carter's repeated public assurances that he is no hurry, the old compulsive U.S. urge for some agreement - any agreement - has returned. The intractable Soviet position at Geneva suggests the Kremlin expects that the American compulsion to back down will yield still more American concessions.

They theory that U.S. negotiators are more interested in the idea of a treaty than what is in it is supported by bargaining over the Backfire bomber. The U.S. proposal accepts the Soviet claim that the Backfire is medium-range and should not be counted in the limit on strategic weapons, even though many experts believe it can reach North America without refueling.

Accordingly, the secret proposal offered in Geneva would "limit" annual Soviet production. Precise figures are top secret, but intelligence estimates of actual Soviet production are but a small fraction of the "ceiling." Further-more, there is no chance Soviet production could even apprach this level during the proposed three years of the limit.

Unlike the Backfire's range, its production is not disputed inside the CIA or anywhere else in the national security bureaucracy. The only reasonable assumption, then, is that the SALT negotiators are guilty of inexcusable slopiness. Nor is the Backfire the only such instance.

Testifying before Sen. Henry M. Jackson's subcommittee, Vance emphasized curbing development of the Soviet Union's huge SS-18 missile. But Pentagon experts feel this shows the U.S. negotiating team is behind the times technologically. The greater menace today is the smaller SS-19, untouched by the proposal.

More significantly, Vance was questioned closely by the senators on whether it would be remotely possible to verify the proposed ban on mobile long-range missiles. U.S. negotiators seem unconcerned that Soviet intermediate-range mobile missiles could be converted to long-range without anybody knowing it.

This helps breed skepticism in the Senate about Vance's reassurances regarding the principal obstacle to a SALT 11 agreement: the U.S. cuise missile. While supposedly postponing testing of land-based and sea-based cruise missiles, the United States does not intend the proposed language to actually block the new wonder-weapons such as the Tomahawk sea-based cruise missile. Whether this is rally so may determine the extent of Senate treaty opposition.

But even if the Senate is convinced that the cruise missile is not endangered, nagging doubts persist about the overriding U.S. purpose. A three-year ban on testing certain cruise missiles and the MX mobile missile would be more acceptable if the time were used to improve the overall strategic position leading to negotiation of a comprehensive SALT II treaty. But there is seemingly no such broad strategy underlying the big push of a SALT II agreement.

Noting U.S. haste, the Russians are characteristically intransigent. For instance, they want restrictions on the U.S. cruise missiles and MX to last for eight years while restraints on Soviet weapons last for only three.

The present SALT climate, therefore, could not be further removed from the Carter administration's hard-nosed beginning in Moscow. Walking backwards, U.S. negotiators offer substantial concessions on their own arms, while asking largely meaningless restriction on Soviet arms. The Russians, patiently awaiting a treaty granting them maximum advantage, have not yet compromised an inch. This climate, rather than the substances of what happened in Geneva, is the source of disquiet in the Senate.