BIPARTISANSHIP in foreign policy is not the same as unanimity in forging that policy. The American public does think its political factions must stick together when it comes to the outside world.
And yet it expects healthy testing debate in Washington rather than unthinking acquiescence to what the White House or Congress, Republicans or Democrats, hawks or doves, think should be done.
So when President Reagan urges more ''bipartisan'' support from Congress for his foreign policy, as he has several times in recent days, he is speaking straight to an ambivalence Americans feel about policymaking.
The fact is, on the really big issues Mr. Reagan has enjoyed vastly more bipartisan support than might appear just by listening to the debate.
On the deployment of intermediate-range missiles in Europe (actually a holdover from the Carter administration), Congress stood with him. Congress went along with his deployment of the Marines in Lebanon; it deferred a review of the deployment until after this year's election. The Senate last week voted $62 million for military assistence in Central America. And so forth.
A fair reading of events is that Congress has conceded to the Reagan White House the right to initiate foreign policy, while assigning the administration the responsibility to prove that the policy will work.
Mr. Reagan complains that chronic congressional second-guessing undercuts his policy. But one must ask, Would any level of silence on the American shores have prevented the Marine pullout from Lebanon?
Sometimes the challenge to the White House can be rough. Sen. Edward Kennedy, leading the unsuccessful Democratic attempt to cut further the Reagan Central America package, said, ''The Senate has voted for wider war in El Salvador, secret war in Nicaragua, and the brink of war in Honduras.''
But such rhetoric can reflect genuine unease among many Republicans as well as Democrats that the United States is traversing a slippery slope of deep involvement of US troops in Central America and interference in the region's political affairs.
Not all members of Congress agree with the administration that the East-West struggle between the United States and the Soviet Union is the overriding issue everywhere - in Central America, the Middle East, southern Africa, the Pacific basin.
Not all members of Congress agree that military force, or deterrence, should play so prominent a role in US foreign policy - in nuclear and chemical arms control, in Lebanon, Central America. Security interests tend to overpower American diplomatic efforts, they think.
President Reagan acknowledged these doubts in his speech Friday at Georgetown University. Still, partisanship ''should stop at the water's edge,'' he urged. And Congress should show a sense of responsibility to match the new power it has asserted since Vietnam.
Expectably, Congress found it could agree with the President's bipartisan foreign policy idealism, while differing on the details of his case.