The State Department reacted yesterday to Senate Minority Leader Howard H. Baker Jr.'s call for modifications in the Panama Canal treaties by restating its position that no changes are needed.

But, despite the stand-pat nature of the department's response, reliable sources said the Carter administration's position is "not cast in concrete" and could be changed if circumstances demand greater flexibility.

First, though, sources added, the administration wants to be sure that any proposed changes are acceptable to Panama and they are needed to win the 67 votes - two thirds of the Senate - required for approval of the treaties.

The position taken by Baker (R-Tenn.) in the upcoming Senate battle over the treaties is regarded as potentially crucial. His support could carry several uncommitted Republican senators into the pro-treaty camp and assure approval of the pacts.

After meeting with Panama's military leader, Gen. Omar Torrijos, last week, Baker said Senate approval would require changes in the treaties signed by Torrijos and President Carter in September. Panamanian officials hinted they were not inflexibly opposed to considering changes.

In particular, Baker seemed interested in finding some way to incorporate a clarifying statement issued by Carter and Torrijas in October.

The statement spelled out U. S. rights to intervene military against threats to the canals after it comes under Panamanian control in the year 2000. It also reaffirmed the right of "head-of-the-line" priority passage for U. S. warships in an emergency.

In addition, Bakaer suggested that the treaties'chances in the Senate would be improved by elimination of a provision preventing the United States from building a new sea-level canal anywhere other than in Panama.

Asked about Baker's call for modifications, department spokesman Hodding Carter III said yesterday that the Carter-Torrijos statement in October had cleared up any questions about U. S. rights in the canal and that further changes are not required.

But, reliable sources said later, the spokesman was repeating standing policy guidance that could be changed after the President and Secretary of State Cyrus R. Vance take a fresher look at the situation.

Carter hinted at such a possibility when he said, "We would be interested to hear what Sen: Baker has to say," Baker, who is visiting several Latin American countries to gauge their views on the treaties, is due back in Washington at the end of the week.

In addition to consulting Baker, the sources said, the administration will have to sound out Torrijos on how he would go in making changes. Also, the sources added, the administration needs to take a new count of how many Senate votes would be swayed by the changes proposed by Baker.

Since Carter and Vance have just returned from their overseas trip, the sources said, they have not had a chance to reassess strategy on the treaties. But, they added, the fact that Vance will undertake a cross-country speaking tour for this week to drum up support for the treaties points to a prompt, high-priority reassessment.