The Carter administration set new terms yesterday for the upcoming presidential debates, insisting that the first confrontation include only President Carter and Republican nominee Ronald Reagan.

In a television appearance yesterday, White House chief of staff Jack Watson said Carter believes it "essential" to have a debate "drawn sharply to show the contrast between the two men and the two parties." Asked whether Carter would insist that the first debate be limited to himself and Reagan, Watson said: "Yes, yes, he would."

Yesterday's announcement was the latest installment in an on-again, off-again effort to isolate independent presidential candidate John B. Anderson by Carter aides fearful that Anderson's candidacy will hurt the president.

The League of Women Voters, which has scheduled three presidential debates -- the first for Sept. 18 in Baltimore -- has said it will include Anderson if he has a 15 percent rating in the popularity polls by Sept. 10.

But Watson suggested on "Face the Nation" (CBS, WDVM) that Carter might meet Reagan in a head-to-head debate before September 18 -- and perhaps not participate in any of the league debates.

Saying the Carter camp "would prefer the debates to begin earlier," Watson said invitations from other groups for Reagan-Carter meetings before then are now "under consideration."

Watson said Carter would be willing to debate other candidates -- including Anderson -- in later meetings.

The league "does not have any franchise on presidential debates," said Watson. "The president has made no commitment whatsoever with the league thus far."

Details about the time, location, format and number of the debates are "items to be negotiated, not mandated," said a Carter-Mondale campaign spokesman.

The league official coordinating the debates said yesterday that "there is a certain amount of flexibility" in the groups arrangements, but that the rules that could resuult in Anderson's participation would not be changed. t

"we've set our criteria," said Ruth Hinerfeld, head of the league's education fund. Hinerfeld said it would be impossible for the league to reschedule its first debate earlier than Sept. 18.

The league official also, said the president had committed himself, at the league's national convention May 5, to participate in the debates. "When asked directly if he would participate, he said 'yes,'" said Hinerfeld.

The baltimore Sun reported yesterday, however, that Reagan and Carter strategists have begun negotiations for a one-on-one session in early September that could force the cancellation of the league's Sept. 18 debate, scheduled to take place in Baltimore. The prospects for the Baltimore debate are now "50-50 at best," an unidentified Carter campaign offical told the newspaper.

Among the prospective alternative debate sponsors are the St. Petersburg Times, the Des Moines Register, and, in possible joint efforts, the Ladies Home Journal with the Women's Economic Roundtable, and Black Enterprize magazine with the Joint Center for Political Studies. It is not known if any of the groups would accept Carter's demand that the first debate include only himself and Reagan.

The Carter camp has tried for months to block a three-way debate that would include Anderson. The effort has been motivated by a belief that the ideologically moderate Illinois congressman would draw more votes from Carter than from the conservative Reagan.

In late May, White house press secretary Jody Powell said Carter would not participate in any debates that included Anderson.Calling it a "fantasy" to believe that Anderson could be elected, Powell said, "it is not our intention to participate in debates with third, fourth, or fifth party candidates."

The statement was viewed as an effort to pressure the league, which sponsored the 1976 debates and was then formulating its rules for the 1980 sessions, to exclude Anderson.

The president stated his position on June 1, when he told a television interview panel: "I see no reason why I should debate against two Repubilcans, who had been active in the Republican Party, who have held positions of leadership in the Republican Party, who have a Republican voting record."

But polls showed Carter's stance was unpopular, and less than two weeks later, he told reporters aboard Air Force one that he would consider debating Anderson, as long as it didn't interfere with a head-to-head confrontation with Reagan.

In August, the league announced its qualifying rules for the debates.

Carter administration officials reportedly have been annoyed by the league's ruling, particularly its decision to give Anderson, whose support has been sagging, until Sept. 10 to achieve the 15 percent rating.

Carter's advisers reportedly believe they would fare better with Reagan in a one-on-one encounter, which would keep the Republican nominee from adopting the above-the-battle posture that he used successfully in multicandidate GOP debates during the primary campaign.

Anderson, responding yesterday to Carter's position, accused the president's advisers of trying "to manipulate the debates in order to benefit Jimmy Carter, even if it comes at the expense of the public." Senior officials in the Reagan campaign were not availaable for comment.