The U.S. Conference of Mayors, feeling pressure from the White House over a scheduling tug of war, abruptly informed Sen. Edward M. Kennedy today that he was no longer welcome to speak here Tuesday -- the same day President Carter is to address the mayors.

The White House told the conference it would be "unacceptable" for Carter and his Democratic presidential rival to address the group on the same day, and the conference then told Kennedy that he could gtive his speech at the convention's closing session here Wednesday.

But a Kennedy aide said late today that the senator would skip the conference and instead deliver his speech on urban issues Tuesday to members of the American Federation of State, County and Municipal Employes, meeting in Anaheim, Calif.

Mayor Richard E. Carver of Peoria, Ill., conference president and a conservation Republican and staunch supporter of Ronald Reagan, would up in the middle of the fray.

"Let's be honest," Carter told reporters of his decision to withdraw the invitation to Kennedy. "It's important for this conference to have the president of the United States.

"Certainly he is one of two [Democratic] candidates but he is also the president."

Carter and Kennedy were to have addressed the convention one hour apart. Carver said the White House had suggested that the president would not appear under those circumstances.

The Great Scheduling Debate, which entailed transcontinental telephone calls between here and Washington all day, enlivened this otherwise subdued five-day annual meeting of big-city mayors.

It also appeared to underscore the continuing rift and rancor between the Kennedy and Carter camps.

The president, who has 300 more delegates than he needs to win the Democratic nomination on the first ballot at the party's August convention, has declared himself the winner of the long primary season. But Kennedy has refused to withdraw and has said the president owes it to the party to debate him in public.

Carter's people have been talking about conciliatory gestures that would bring together Kennedy's more liberal supporters with Carter's backers and avoid a damaging split at the New Yori City convention.

But when conference staff members told White House aide Jane Hartlely today that Kennedy would be speaking shortly after the president on Tuesday, she termed the arrangement "unacceptable," according to Tom Cochran, deputy executive director of the conference.

Orginally, Carter was invited to speak here today and Kennedy Tuesday. Cochran said the White House informed his late last week that the president would be available Tuesday, but not today. At that time, he said, he had no firm commitment that Kennedy would attend, but the senator's aides in Washington said that if he could it would probably be on Wednesday.

Kathy Garmezy, a member of the Kennedy advance team here, said that Wednesday was never acceptable to the senator because she had learned that many mayors will have lift Seattle by then.

She described the White House pressure on the conference as "a pretty heavy number.It's not even an issue of not debating. It's an issue of letting other people speak before groups."