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Jeff Weaver, the campaign manager for Senator Bernie Sanders, said on Tuesday evening that Mr. Sanders did not want to participate in an unsanctioned debate next month because he could risk being denied participation in future debates.

The debate would be held Feb. 4 in New Hampshire, five days before the state’s primary. It would be sponsored by MSNBC and The New Hampshire Union Leader, which announced that the “Meet the Press” host Chuck Todd and the MSNBC anchor Rachel Maddow would moderate the debate.

The Democratic National Committee has “said this will be an unsanctioned debate, so we would not want to jeopardize our ability to participate in future debates,” Mr. Weaver said.

He added that if the Democratic National Committee did sanction the debate, the campaign’s stance would be different.

Jen Palmieri, a spokesman for Mrs. Clinton, told The Union Leader, “Hillary Clinton would be happy to participate in a debate in New Hampshire if the other candidates agree, which would allow the D.N.C. to sanction the debate.”

John Bivona, a spokesman for the candidate Martin O’Malley, the former Maryland governor, told the paper: “Today is a big victory not only for our campaign and our supporters that championed this effort, but it is also a victory for voters across New Hampshire and the United States. We look forward to participating.”

Mr. Weaver, the Sanders campaign manager, said that what is needed “is a rational, thought-out schedule of debates. Not just ad hoc debates scheduled whenever a network decides they want to have one.”

He added: “All of the candidates are going to be together the next night at the Democratic dinner in New Hampshire. We look forward to meeting them in debates in Wisconsin, in Florida, and then at least three or four more after that.”

Mr. Weaver said Mr. Sanders’s campaign had not discussed the possible unsanctioned debate with Hillary Clinton’s campaign.

He said: “We think there should be at least three or four more debates following the ones that are currently scheduled. Senator Sanders has wanted more debates from the beginning of this campaign, and we are happy to see that it looks like we are likely to get them.”

Mr. Weaver also expressed frustration at the way the possible addition of a debate had been handled.

“We want a schedule of debates,” he said. “This ad hoc adding a debate when somebody wants it is not a good way to run things.”

