A dispute between the White House and the Senate Foreign Relations Committee has bottled up a priority item in President Carter's foreign policy-U.S. adherence to a treaty banning nuclear weapons in Latin America.

Carter signed the last of two protocols linking the United States to the Latin treaty two years ago but has failed to move the Senate to advise ratification.

The treaty is little known in this country, partly because it goes by the nearly unpronounceable name of Tlatelolco-for the locale of the Foreign Ministry in Mexico, which initiated the pact in the mid-1960s.

However, U.S. experts on nuclear nonproliferation agree on the importance of the treaty, which prohibits "testing, use, manufacture, production or acquisition by any means whatsoever of any nuclear weapons" in the vast zone south of the Rio Grande River.

The treaty is now in force among 21 Latin and Caribbean nations. While the United States is not a party to the treaty itself but only the protocols, U.S. envoys are actively encouraging the last two Latin holdouts-Argentina and Cuba-to adhere to the pact.

Argentina-which along with Brazil is believed to be capable of producing nuclear weapons-has yet to ratify although its military government has stated its intention to do so.

U.S. pressure on Argentina is undercut by the failure of Washington to follow through on ratification.Argentine adherence is critical because two other key states, Brazil and Chile, used the treaty's unusual option of ratification while withholding actual participation until all signatories have done so.

In the case of Cuba, the United States has encouraged pressure on Havana from the Soviet Union - which, like all affected outside powers except the United States and France, has adhered.

France is on the verge of completing its ratification so the United States could end up as the last holdout even though successive administrations have given the pact at least lip service since it was opened to signature 12 years ago.

While the treaty is open only to nations in the Latin zone, it carries two protocols, both affecting the United States and one of which still requires Senate approval:

Protocol I obligates outside powers with territories in the zone to apply denuclearization to those territories. Thus the United States could not station nuclear weapons in Puerto Rico or the Virgin Islands, or at Guantanamo Bay Naval Base if Cuba joins the zone. This is the protocol awaiting U.S. and French ratification.

Protocol II prohibits existing nuclear powers from introducing such weapons into the zone. The United States ratified it in 1968, the first limitation placed on deployment of the American nuclear arsenal. Mexican persistence has also gained the unique adherence of both China and the Soviet Union, along with Britain and France.

The treaty has its policing unit and obligates Latin nations to submit their peaceful nuclear programs to regulation by the International Atomic Energy Agency.

Sea or air transit privileges of U.S. weapons are not affected.

Sen. Frank Church (D-Idaho), chairman of the Foreign Relations Committee, calls the pact "a very significant arms control initative" that "may yet serve to set a precedent for similar initiatives elsewhere."

But Church has balked for reasons that have more to do with executive privilege and the independence of the Joint Chiefs of Staff than with the treaty itself. And this dispute could even affect the Senate's receptivity to the eventual strategic arms limitation treaty (SALT II) between the United States and the Soviet Union.

Trouble began with a memo signed by national security adviser Zbigniew Brzezinski to Secretary of Defense Harold Brown last Aug. 7, just before long-sought hearings by the committee on Protocol I.

The memo remains emphatically confidential but the operative sentence of its two paragraphs states:

"I know that you are aware of the importance that the president attaches to the ratification of Protocol I and that you will ensure that the representatives from your department and the Joint Chiefs of Staff who will testify before the committee will indicate their complete and unequivocal support for the treaty."

The memo leaked to columnists Rowland Evans and Robert Novak, who quoted the phrase about "unequivocal support" to demostrate a new get-tough policy by the White House against dissent on policy.

Protocol I thudded into a pigeon-hole as the committee staff recommended no action until the memo was obtained. With Brzezinski's team defending the concept of executive confidentiality, the State Department asked Church what could be done.

Church noted in reply the irony that, according to the chairman of the joint chiefs, the military had decided to advocate ratification a full eight months before Brzezinski's memo.

"Without having the memorandum in hand," said Church, "it is impossible for the committee to ascertain whether the purpose was simply to seek support which had already been given or to influence the character and degree of the joint chiefs' support. . ."

According to committee staff members as well as State Department officials, there is concern that opponents of SALT II will use the Latin treaty memo to question whether the joint chiefs can freely state their views on SALT II.

National Security Council officials will make no comment, not even to acknowledge the existence of the memo. Unofficially, they suggest that the committee is trying to shift the blame for its own inaction.

A State Department official, who in this context occupies a middle ground, said he believes the White House did not mean to intimidate the joint chiefs but simply let unfortunate phrasing escape unedited.

Although the memo bore Brzezinski's name, it was drafted by his specialist on Latin America, Robert Pastor. He has been praised for the intensity of his efforts on Latin policy but criticized for inexperience.

At 32, he is younger than most staffers at his level. "It is a mistake to put a person of limited experience in a job of that importance, and it shows," said a State Department official familiar with the dispute.

So a process that started 12 years ago still falls short in Washington. At the 1967 signing in Tlatelolco, Mexico's chief negotiator, Adolfo Robles Garcia, had predicted the process could take only two years.

U.S. diplomats were skeptical about that, with reason as it turned out. But not many of them foresaw such widespread adherence - or that their own government might hold it up.

When the chances for Senate action looked brighter last August, it was thought that Carter could make the formal ratification during his projected visit to Mexico.

Accordingly, the Carters' visit - which got mixed reviews - began on Feb. 14, the 12th anniversary of the treaty with the unpronounceable name.