Harmonious relations with Congress in foreign policy was a repeated promise of the Carter campaign. But the Carter administration finds itself at odds with Congress on every international issue. How come?

Weak leadership in the Senate and misplaced priorities by the administration count for something. But the parent difficulty is that Congress has over-reached itself in foreign policy and must now be gentled back to a more appropriate - which is to say modest - role.

The signs of the trouble go round the globe. The administration's effort to rush the Panama Canal treaties through the Senate has collapsed, and there is no prospect of ratification until next year, and maybe even late next year.

The arms-control agreement due out of Geneva any week now has already stirred opposition from Sen. Henry Jackson, the powerful Washington Democrat, and a Republican group led by presidential aspirant Bob Dole of Kansas. Every initiative in the Middle East brings squawks from pro-Israeli hawks - squawks that have already forced the administration back several paces.

Human rights - the "motherhood" issue in foreign policy - has also been turned against the administration. It held up and nearly crippled the foreign-aid bill and threatens (along with the Tongsun Park case) relations with South Korea.

The administration has even been harassed on the most innocuous arms sales. It took several months and the special intervention of Hubert Humphrey to win approval for sale of an air defense system to Iran, a friendly country crucial for order in the Persian Gulf and the Arabian Sea.

Sen. Humphrey's role in the sale to Iran points up one genuine problem. He is ailing, and the chairman of the Foreign Relations Committee, John Sparkman of Alabama, shows every minute of his 77 years. Majority Leader Robert Byrd has no expertise in the international arena, and none of the senators who appeared to be coming forth in the past decade have actually emerged. Indeed one of the spectacles afforded by the Panama Canal hearing has been that of famous Senate doves on Vietnam hiding behind the testimony offered by two former Secretaries of State - Dean Rusk and Henry Kissinger - who were once reviled for being what Rusk called "too hard-boiled."

The administration has made matters worse by tactical mistakes. The treaties with Panama entail eventually giving up something believed by many people to belong to this country as much as the flag. No amount of spectacular signing ceremonies or committees of Beautiful People can convert the treaties into winners.

So Panama has been a poor choice to head the administration's agenda for congressional support in foreign policy. Far better would be to make the arms-control treaty now shaping up the priority business.

Arms control, unlike the Panama treaties, is thought by most Americans to be important and urgent. If not exactly popular, it is at least so complicated that mounting opposition becomes hard.

Still, the true problem is history - not Senate leadership or administration tactics. The systematic deceptions of the Johnson and Nixon administrations - the revelations about wiretaps, assassinations and all that dirty business - forced the Congress to assert itself. It did so, particularly on Vietnam, with success.

In consequence, the national-security mystique whereby a President was generally given the benefit of the doubt has been shattered. Now foreign-policy issues, like pork-barrel issues, have become a fit subject for legislative wheeling and dealing.

Small, one-issue groups, as a result, can make the kind of alliances that give them something like veto power. A hard core of conservatives has converted Panama into a big deal, with potentially telling effect on the 1978 congressional elections and the Republican nomination for President in 1980. The Israeli lobby does the same on the Middle East, the hawks on arms control, the Greek lobby on aid to Turkey, and so forth.

Congressional foreign policy - or more exactly, domination of foreign policy by the one-issue interests given so much prominence in the congressional process - is a recipe for paralysis, and ought to be ended. But President Carter has reaped the whirlwind of mistrust sown by the Johnson and Nixon administrations. He can rebuild trust in national security only by a long, slow process of give and take with the Congress. Which means that the President has to school himself to argue - and indeed, think - in terms of modest progress toward distant goals.