President Carter's endorsement of "a homeland" for the Palestinians in his remarks at Clinton, Mass., Wednesday night was an innovation in American definitions of terms for an Arab-Israeli peace settlement, administration officials acknowledged yesterday.

Officials said the president's terminology was calculated, and not casual, and described it as a perhaps noteworthy shift of langudage.

Arab leaders were pleased; Israelis ere chagrined. Ten days ago, the reactions were the reverse when Cater endorsed "defensible borders" for Israel. The Israelis were delighted, the Arabs dismayed, although two days later the president qualified his language on borders, and Iraeli elation diminished.

A State Department spokesman yesterday was besieged by questions about the implications of the President's support for a Palestinian "homeland" - which caught at least some State Department officials by surprise.

Traditionally, the United States has employed much more ambiguous language on this diplomatically explosive issue. In recent months, U.S. officials have expressed support for the "legitimate interests" of the Palestinian people - which they have refused to define further, to avoid being caught between the opposing Arab and Israeli postiions.

State Department spokesman Frederick Z. Brown initially refused to say yesterday if the term "homelands" represented a change in U.S. policy.

Late, to quell Israeli alarm, the spokesman, after consulting with superiors, stated flatly that "there has been no change" in U.S. policy.

The bitterest political issue in the Arab-Israeli conflict is whether there will be a separate state of homeland for the Palestinians, and what it will comprise, geographically."

In an interview in July, Carter said:

"There ought to be territories ceded for the use of the Palestinians." He said "my own preference" would be that "they should be part of Jordan and be administered by Jordan." This is more in line with approach that Israel favors.

En route to New York, Carter told reporters aboard Air Force One that his call for a "homeland" was "approriate," although it has disturbed Israeli leaders.

"I think some provision has got to be made for the Palestinians.In the framework of the nation of Jordan or by some other means," he said. He did not elaborate.

This partial reversion yesterday to what Carter had said during the presidential campaign now may possibly diminish the original Arab pleasure with what Carter said Wednesday night.

On Wednesday night Carter said "the first prerequisite of a lasting peace is the recognition of Israel by her neighbors . . . Israeli's right to exist in peace . . . The second one is the establishment of permanent borders for Israel . . . And the third ultimate requirement for peace is to deal with the Palestinian problem . . ."

"The Palestinians," he noted, claim "that Israel has no right to be there" and "they have never yet given up their publicly professed commitment to destroy Israel. This has to be overcome.

"There has to be a homeland provided for the Palestinian refugees who have suffered for many, many years . . ."

Spokesman Brown, and officials accompanying the President, stressed, however, that this "does not imply that the United States takes a position on what form it [the 'homeland'] will take."