The historic Senate debate on arms control is being inexorably delayed, perhaps into next year beyond the 1978 elections, thanks to developments in Washington and Geneva tied to a single word: verification.

In Washington, prospects for Senate ratification of a new SALT (strategic arms limitation talks) agreement are going down instead of up because of serious doubts about Soviet compliance. In Geneva, U.S. efforts at verification are partly responsible for unexpected delay in negotiating an agreement.

Central to this problem is the Soviet Backfire bomber. The Senate insits on verification that the bomber will not be an intercontinental weapon, the difficulty of which has stymied the U.S.-Soviet talks. The U.S. effort to bar modernization of strategic weapons, another unresolved point, also reveals the limits of verification.

But questions larger than verification are raised. Does the willingness of U.S. negotiators to accept the Backfire as a non-strategic weapon betray over-eagerness for agreement? Is the U.S. attempt to bar modernization an effort to compensate for the vulnerability of U.S. minuteman strategic missiles?

Indeed, expert critics of the nearly completed SALT II agreement feel it gives the Kremlin a dangerous strategic advantage even if all limits on the Soviets could be verified. But it is verification, more understandable to the layman, the causes unease among uncommitted senators - particularly John Glenn (D-Ohio).

Having supported chief SALT negotiator Paul Warnke in his closely contested confirmation fight, Glenn was counted on by the White House as a vote for ratification. But after attending the Geneva negotiations as a Senate observer, the former astronaut came away worried about verification. Unless restrictions on the Soviet Union are made more verifiable than they are today, Glenn will vote no on SALT II.

Consequently, senior administration officials are in no hurry for a SALT ratification debate and would prefer waiting until after the 1978 elections. This lack of haste is one reason why the old Carter administration forecast that a SALT treaty would be initialed this month is now inoperable.

Moreover, the Backfire bomber issue remains a serious stumbling block. The Backfire clearly has the range to reach North America on a one-way flight. The Russians insist it is not a strategic weapon, will not count it in SALT's numerical limitation on strategic weapons, and will not even mention it in the Salt II agreement. Instead, they offer a letter from President Leonid Brezhnev promising not to use the Backfire as an intercontinental weapon.

In a recent interview over RKO general television, Warke told us any Backfire agreement "will have to be something which is legally binding and which is verifiable." What the U.S. has in mind is co-signing Brezhnev's letter to make it "legally binding." But even putting it into the agreement itself would not guarantee against the Russians turning the Backfire overnight into a strategic weapon. In short, it is not verifiable.

Simultaneously, Soviet negotiators use the non-verifiable argument in resisting U.S. demands to prohibit modernization of intercontinental missiles. This demand is intended, by preventing Soviet modernization, to bolster the largely discredited argument by the arms-control community that SALT II would contain the Soviet threat to minuteman silos.

But Soviet negotiators are adamant. On recent official cable back from Geneva describes this position by Soviet negotiator Shchukin: "Freezing any improvements to existing ballistic missiles (for example, guidance) was impossible and unverifiable. Any military man who wanted to introduce improvements to his system could do so, could not be stopped, and it was absolutely unverifiable." The Russians are saying: We couldn't stop our military if we wanted to.

If missile improvements are unverifiable, why should the Russians complain? The suspicion is that Moscow plans such extensive modernization of missiles that some of it would surely be observed. Thus, the real concern raised by SALT II is not just lack of verification but the Soviet Union's implacable improvement of strategic systems while the U.S. scraps the B-1 bomber, slows development of the MX mobile missile, and agrees to limit cruise missile development.

In reply Paul Warnke is know to feel there must be some measure of confidence in Russian good faith. But if such confidence is all that is necessary, the entire tedious procedure of SALT negotiations would seem superfluous. The fact is that Glenn and many other fence-sitting senators lack Warnke's measure of confidence in the Russians, and that is the basic reason why the administration is by no means ready for a SALT debate in the Senate.