Senate action yesterday on policy toward Korea and Cuba reflects congressional concern that President Carter may be departing too far, too fast from longstanding U.S. anti-Communist positions.

The Senate's refusal to support Carter's plan for withdrawing U.S. ground troops from South Korea or to allow the sale of medical supplies and food to Cuba represent an abrupt step away from traditional U.S. policy toward both countries.

The Senate's position that the Korea troops withdrawal should be a "joint decision" by Carter and Congress is a shot across the presidential bow by conservatives who doubt that the withdrawal plan should be carried out.

The legislative development enhances the importance of forthcoming hearings in the Senate and House on the Korean withdrawal, including Senate Foreign Relations Committee testimony scheduled for Monday by CIA director Stansfield Turner, who is known to have expressed his own reservations about the plan in National Security Council deliberations.

Some of Carter's major Democratic supporters in the Senate conceded that they do not know exactly what the President's policy is or what it is based on. Thus, in their view, an endorsement of that policy would be premature.

Republican critics, charging Carter with attempting hasty fulfillment of an ill-considered campaign promise to withdraw troops, believe he may be politically vulnerable on the issue. The taste of political blood may add to their own doubts about the policy.

Congressional insistence that U.S. ground troops remain exposed in South Korea despite the plans of a Democratic President would seem inconsistent with congressional action under Republican Presidents to halt U.S. involvement in Vietnam and head off intervention in Angola.

It seems doubtful that Congress will stop Carter on the Korean troop withdrawal, but yesterday's voting indicates that the legislators will have to be convinced.

On Cuba policy, congressional doubts were expressed privately but forcefully a week ago in a presidential meeting with Senate and House leaders of both parties. Informed sources quoted Carter as saying he had no intention of taking further steps toward improving relations until a favorable response is received from the Cuban side.

Carter's private statement was quickly passed to the executive branch bureaucracy, where it has been accepted as an indication of policy. It also became widely known at the Capitol and was a factor in yesterday's maneuvering.

Carter promised Sen. George McGovern (D-S.D.) several months ago that he would not oppose a partial lifting of the trade embargo against Cuba, and McGovern said yesterday that Carter had kept his word. However, Carter also did not propose or endorse such an action, and its opponents used that non-endorsement as an argument that it should not be done. Carter's statement to the leaders last week was cited as a further reason not to temper with the Cuban embargo.

A National Security Council review early this year ended with the presidential decision to seek improved relations with Cuba "on a measured and reciprocal basis." Administration officials said this arose from Carter's belief in diplomatic contacts with all nations as well as from a judgement that the U.S. attempt to isolate Cuba has failed.

There was relatively little domestic opposition to the first steps - maritime and fishing pacts, and the limited exchanged of diplomats assigned as "interest sections" in the two capitals. An attempt last Friday in the House to block the diplomatic exchange was voted down by a surprisingly large margin, 203 to 139.

There is greater controversy about further steps. Fifty U.S. corporations with unpaid claims for nationalized property, for example, lobbied Congress against any lifting to the trade embargo at present. Former Secretary of State Henry A Kissinger opposed normalization of relations until Cuban troops withdraw from Africa.

Showing reluctance to force a confrontation with Carter, the Senate voted down tough and explicit preconditions for new steps toward Havana. As in the case of Korea, however, the net result was a warning to Carter to proceed with caution - and with the lawmakers fully consulted.