The US Congress is reaching for a larger role in foreign affairs. This is manifesting itself in at least four ways:
* President Reagan wants defense spending increased 10.2 percent after inflation. But the Democratic leadership in Congress proposes around 4 percent, and a comprise of around 7 percent is possible. As submitted, the '84 defense budget is around $280.5 billion.
* Congress feels the pressure of the widespread nuclear freeze movement; some expression of that sentiment is likely to come to a vote.
* Tensions over global arms control have had various outlets, such as during the confirmation hearings of Kenneth L. Adelman, Mr. Reagan's nominee to head the Arms Control and Disarmament Agency.
* Congress wants to know what's going on in El Salvador, and the relationship of the US with Caribbean countries is likely to be explored.
Reagan has generally taken a hard line toward the Soviet Union, often expressed in his utterances. Congress has watched restlessly. He has not always been able to make his policies prevail abroad, as when he retreated after trying to get European allies to oppose the Soviets on the gas pipeline from Siberia.
Now a major issue looms - the question of American deployment of new nuclear weapons in Europe and Asia. What amounts to a global test of firmness is underway, some feel, with Mr. Reagan laying down his terms in his arms control policy speech in Southern California March 31, and Soviet Foreign Minister Andrei A. Gromyko answering in Moscow April 2.
The House of Representatives had seemed close to approving a resolution in favor of a nuclear ''freeze'' in March, but put off the vote until it returned after Easter. Reagan says such approval would embarrass him. Tension has heightened; Congress has been back home talking to voters. It wants more consultation with the President and has the means to get it. Reagan's task is to persuade Congress to go along with the rest of the country.
''I don't think the administration has any choice but to listen to us,'' said Senate Foreign Relations Committee chairman Charles H. Percy (R) of Illinios. ''They can't spend money we don't appropriate. We have a role to play.''
The Constitution, political scientist James L. Sundquist notes, ''did not give the country a single voice in world affairs. It established three separated power centers - a Senate and a House of Representatives as well as a president. If it gave the executive some exclusive powers it gave the legislative bodies some as well, including the appropriation of funds and, most important, the ratification of treaties.''
Sen. Barry M. Goldwater (R) of Arizona said in 1976, ''Congress should not assert its distinct power, but should realize that a single elected official, who would not be disturbed by the politics of the moment, would use these powers far more wisely.''