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Two vice chairs of the Democratic National Committee are publicly calling on the party to increase the number of presidential debates, adding high-profile voices to efforts to change the process.

Representative Tulsi Gabbard of Hawaii and R.T. Rybak, a former mayor of Minneapolis, released a joint statement late on Wednesday urging the party committee to remove the restrictions that were put in place to prevent presidential candidates from taking part in unsanctioned debates. The schedule has been criticized by Martin O’Malley, a candidate and former governor of Maryland, as too restrictive, and by some Democrats as being too favorable to Hillary Rodham Clinton.

The party committee’s “decision to limit Presidential candidates to 6 debates, with a threat of exclusion for any candidate who participates in any non-DNC sanctioned debate, is a mistake,” Ms. Gabbard and Mr. Rybak wrote in their statement.

“It limits the ability of the American people to benefit from a strong, transparent, vigorous debate between our Presidential candidates, as they make the important decision of who will be our Democratic Presidential nominee,” they wrote.

“As vice chairs of the Democratic National Committee, we are calling for several more debates than the six currently scheduled, and withdrawing the proposed sanctions against candidates who choose to participate in non-DNC sanctioned debates,” they wrote.

The two added, “We are the party that represents democratic principles, openness and transparency, and ensuring that all people, regardless of who they are or where they are from, have a level playing field and equal opportunity.”

Their argument echoes a speech given at the party’s summer meeting in Minnesota by Mr. O’Malley, who has been struggling to gain traction in the polls.

Supporters of the current system say the candidates agreed to the debate restrictions, something that some of the campaigns dispute, saying they didn’t agree to all the terms. Mrs. Clinton’s campaign had favored fewer and Mr. O’Malley wanted as many as a dozen. Senator Bernie Sanders of Vermont has also called for more debates, although he has declined to join with Mr. O’Malley in pressing for them.

In previous campaign cycles, there have been roughly the same number of sanctioned debates. But the candidates also took place in many unsanctioned debates, without fear of exclusion from the sanctioned ones.

Officials with the party committee declined to comment.

Democratic officials close to the process have said the desire was to keep the voting season from becoming a circus. But critics have said it gives an unfair advantage to Mrs. Clinton.

While Mr. O’Malley’s calls have been the loudest, there have long been vocal complaints from New Hampshire activists who are upset that their lone debate is taking place between the Hanukah and Christmas holidays, a time when people are likelier to be distracted by family obligations.

It is widely believed that if Vice President Joseph R. Biden Jr. decides to run for president, he will ask for more debates and that he will likely get them.

In recent days, Mrs. Clinton has suggested that she would be open to having more debates if that’s what the party committee decides to do.

Two other vice chairs declined to endorse the call from their colleagues to immediately reopen the process.

Donna Brazile, the campaign manager for Vice President Al Gore in 2000, said that though she sympathized with both sides of the issue, increasing the number of total forums, as opposed to just the debates, should be addressed, especially to counter the noise and energy generated by the broad Republican field.

Ray Buckley, the chairman of the New Hampshire Democratic Party and another vice chair, said that he thinks there will be many chances for the candidates “to get their message out.”