The Soviet Union has sent less than a squadron of Mig 23 warplanes to Cuba.

This much is agreed upon by officials within the government and hardliners outside it. But that is about all they do agree upon.

The breadth of the disagreement was dramatized yesterday as the former head of the Defense Intelligence Agency and the current secretary of state exchanged fire on the Mig 23 issue.

Retired Lt. Gen. Daniel O. Graham, who headed the DIA from 1974 to 1976, charged during a press conference sponsored by the American Security Council that the Carter administration was "covering up the rather dangerous breach of the Kennedy Khrushchev agreement" banning the deployment of offensive weapons in Cuba. The council is conservative in its politics and favors a tough policy toward Cuba and its Soviet patrons.

That part of the agreement stemming from the Cuban missile crisis of 1962, Graham said, was breached as far back as July when the United States government detected crates of Mig 23s going into Cuba but did not disclose them to Congress and the public.

The administration's "next effort," Graham predicted, "will be to convince Congress and the public that the presence of this aircraft in Cuba is a little consequence," that its presence on the island does not violate the 1962 agreements.

Secretary of State Cyrus Vance, when asked about Graham's cover-up charge, said: "It's simply untrue." Administration officials insist, they are not yet sure whether the Mig 23s sent to Cuba are the type designed for offensive bombing or for air defense.

The fact is that it really does not make much difference if the Mig 23s turn out to be the versions the Soviets use for air defense or the ones tailored for bombing. Bombs could be strapped on either type.

The significant military question is whether Soviet Mig 23s in Cuba pose a meaningful threat to the United States. The present force of about 10 Mig 23s, which could fly only about as far from Cuba as Jacksonville, Fla. in a round-trip bombing mission, certainly could not be considered a grave military threat to the United States.

Would Cuban leaders, or their Soviet backers, declare war on the United States with a puny force of fighter bombers that could fly no father than Florida? Would those leaders risk nuclear incinaration of their own countries by dropping tactical nukes on Florida? There are no U.S. missile bases in Florida to attack.

It is true, as Graham warned yesterday, that penetration of U.S. air defenses is easy for an enemy plane, even easier for a missle. The United States and Soviet Union rightly or wrongly, have opted for offense rather than missile defense in this nuclear age.

All this does not mean the United States would sit idly by and watch Cuba become an armed camp. But the 10 Mig 23s in Cuba today, plus the Soviet Osa class gunboats on the way there, which carry Styx anti-ship missiles with a range of about 20 miles, do not add up to an armed camp.

Graham conceded at his press conference that Cuba does not intend to attack the United States, whether or not it has Mig 23s tailored for carrying nuclear bombs. So why, at this delicate moment, is the Soviet Union sending Mig 23s into the backyard of the United States?

Apparently no U.S. officials know the answer for sure. But it has to be political reason - not a military one since going to war simply does not make sense.

Perhaps, is exchange for sending Cuban troops into Africa, the Soviet Union agreed to modernize Centre air force and navy. The United States to cite a parallel, felt obliged to modernize Taiwan's air force even though Peking worries about this.

Or perhaps Graham is right in asserting that the Soviets are arming Cuba to "dramatize" the "impotency" of the United States and to test President Carter.

Whatever the real reason, Migs in Cuba today cannot be equated with the missiles the Soviets put there in 1962 when, according to President Kennedy, the resulting U.S.-Soviet confrontation posed a 1-in-3 chance of leading to allout war.