The US Senate will ratify just about any arms control treaty that American delegate Paul Nitze approves at Geneva in negotiations with Moscow. The reason: Hawks in the Senate, who have a veto power over armament control treaties, have confidence in Mr. Nitze, who is a hawk himself.
Richard Nixon was able to reach agreement with Communist China, and to pave the way for detente with the Russians, which the liberal Democrats could not have achieved since they were always suspected of being ''soft on communism.'' In the same way the Reagan administration is better able to hold conservatives in line in the Senate, if any agreement with the USSR is possible.
A Senate vote of one-third plus one, or 34, can veto a treaty under the Constitution. This gives Senate conservatives the balance of power. This veto power kept the US out of the League of Nations in March 1920, although there was always a Senate majority for the league. It stalled Senate ratification of the SALT II arms control agreement in 1981, signed by President Carter, when feelings chilled after the Soviet invasion of Afghanistan.
It will hardly affect President Reagan, however, because of his own stern attitude toward communism and because of the hawkish approach of negotiator Nitze and his colleagues at the Arms Control and Disarmament Agency.
The triumvirate of the Reagan Arms Control Agency is as implacably anticommunist as any conservative senator could ask:
* Eugene V. Rostow, former Yale Law School dean, is director of the agency. A one-time adviser of Lyndon Johnson in the State Department, he became chairman of the Committee on the Present Danger which helped block the SALT II treaty.
* Lt. Gen. Edward L. Rowny (US Army ret.) is a one-time representative of the Joint Chiefs of Staff in the SALT discussions who resigned to campaign against the accord.
* Paul H. Nitze, former secretary of the Navy and deputy secretary of defense under Lyndon Johnson, was an architect of the original (Nixon) SALT agreement and then became a leading opponent of the Ford-Carter SALT II.
In the present Geneva talks Mr. Nitze is the chief negotiator for a special category of nuclear weapons, those with intermediate range known as Theater Nuclear Force. Geneva will see in him a forceful white-haired figure, with strongly lined face, urbane manner, and a bewildering technical knowledge of nuclear and conventional weaponry. He has been described as the quintessential hawk and a flinty veteran of talks with the Russians.
The Reagan administration's attitude toward the Soviet Union began with the Republican convention in 1980 in Detroit, which demanded arms superiority, not equality, with the USSR and charged Democrats with softness. Mr. Reagan says Moscow must be dealt with from a position of strength. In October 1980, however, he said that if elected ''I will immediately open negotiations on a SALT III treaty. My goal is to begin arms reductions.''
After the election Europe waited for arms discussion and a mood of neutralism and neo-isolationism grew. Some statements by Mr. Reagan and Cabinet members indicated belief in the possibility of a limited nuclear war.
Addressing the party congress in Moscow, Feb. 23, Mr. Brezhnev asserted that ''candidly bellicose calls and statements have resounded from Washington, especially designed, as it were, to poison the atmosphere.''
Private Reagan-Brezhnev letters, it is disclosed, simultaneously discussed the possibility of arms discussion and a direct summit meeting later. For the moment the discussion turns to Mr. Nitze.