President Carter, working to boost the morale of his supporters, said yesterday that the Republicans had engaged in a "debacle" at their convention in Detroit in attempting to enlist former president Ford as Ronald Reagan's vice presidential running mate.

Making his first public comments on the unsuccessful negotiations between Reagan and Ford over the sharing of presidential responsibilities, Carter told about 200 Democratic National Convention delegates pledged to him:

"The Oval Office is not something to be traded in a hurried fashion in the middle of the night."

The Carter delegates, from 18 states and three territories, gathered in the East Room of the White House to enjoy a cheese and wine buffet and hear from Carter after a day of briefings by White House and Carter campaign officials.

The day of briefings by such administration officials as Treasury Secretary G. William Miller and national security affairs adviser Zbigniew Brzezinki was designated to solidify the president's support for a final challenge from Sen. Edward M. Kennedy (D-Mass.) at next month's Democratic National Convention in New York.

Similar sessions are planned for other Carter delegates Friday and Aug. 1.

Aaron Henry, a longtime civil rights worker and Carter delegate from Mississippi, said the day of briefings was "sort of a pep rally" at which campaign officials reviewed the likely minority reports on the party platform and the convention rules.

He and other delegates said they were urged to resist efforts by Kennedy's supporters to change the rules under which delegates are bound to the candidate who won the primary or caucus in their state.

Judging by the enthusiastic cheers that greeted the president and his wife, Rosalynn, in the East Room, there is little chance Kennedy could make inroads among the group invited to the White House yesterday.

For his part, Carter confined his references to Kennedy to an appeal for party unity and a caution to his supporters not to let their emotions get out of hand in New York.

"Although we might be debating against them (the Kennedy supporters) in New York, we'll be working with all of them throughout the country in November," he said. "So keep that in mind. We'll all win together."

While he said he had not watched the Republican convention on television, the president had clearly studied the convention's makeup. He asserted that the average income of the GOP delegates was $50,000 a year and said there was little debate among them because there are "no issues" dividing such a narrow segment of American society.

There will be debates in New York, he said, but this "is not a sign the Democratic Party is weak and it is not a sign the Democratic Party will be divided in November."