Democratic Party officials say they will not release the names of donors to next month’s political convention before the event, despite an earlier pledge that they would regularly disclose the contributors.

In its marketing materials, the party promises that the “people’s convention,” set to begin Sept. 3 in Charlotte, will be the “most open and accessible ever.” But the names of donors, some of whom are giving up to $100,000, will remain secret until federal disclosure documents are filed Oct. 15, six weeks after the festivities have ended, when public attention will have shifted to Election Day.

Democrats have made transparency a central theme of the campaign, pushing for legislation requiring groups to disclose donors. In a recent e-mail to supporters, President Obama’s campaign manager, Jim Messina, asked for signatures on a petition calling for conservative interest groups to reveal the names of contributors.

“They have a vested interest in being able to spend millions anonymously to influence our elections,” Messina wrote.

The Obama campaign and its supporters also have called on Republican challenger Mitt Romney to release more tax returns, suggesting that he may be hiding information about his personal finances.

Four years ago, both parties voluntarily listed convention donors online and made regular updates to the information.

Sheila Krumholz, executive director of the nonpartisan Center for Responsible Politics, said the decision not to disclose donors until October “just seems to run counter to the message that this is the people’s convention. You’d think transparency would be something celebrated, not reduced.”

Democrats have had trouble raising money for the gathering largely because of a decision to ban corporate money. Corporations traditionally have provided much of the financing for both party conventions. But in a sign of their tight budget, Democratic organizers shortened the official convention schedule from four days to three.

The host committee for the convention, known as Charlotte in 2012, had published on its Web site its policy that donors would be disclosed online “on an ongoing basis.” And the contract that city officials signed with Democratic Party officials specified that “all contributions, monetary or in-kind, shall be disclosed publicly . . . within an agreed upon regular timeframe on the host committee’s website.”

The committee removed that language from its Web site last week after an inquiry from The Washington Post.

A spokeswoman for the committee, Suzi Emmerling, said in an e-mailed statement that the site “has not been updated for some time and is not consistent with our current policies. Our current policy is that we will file a report and make information available compliant with FEC guidelines.”

Emmerling said that the host committee and Democrats decided that the “regular timeframe” to disclose was by the date it was required by federal law.

Obama campaign spokesman Ben LaBolt declined to comment.

Joanne Peters, a spokeswoman for the Democratic National Convention Committee, declined to comment about the disclosure of donors. She said in an e-mailed statement that “the DNCC has instituted the strongest and farthest-reaching rules ever established governing fundraising and special interest access at a convention.”

The host committee for the Republican convention in Tampa did not pledge to disclose donors and does not mention its individual contributors, but it does display on its Web site logos from 26 corporate sponsors, including Google and Wal-Mart.

“We display our sponsors because they’ve been supportive of our Tampa Bay community,” said Ken Jones, the head of the Tampa Bay Host Committee. “We’re proud to have them.”

The Charlotte host committee, in an agreement with the Democratic Party, banned direct corporate donations but accepts corporate donations of goods and services. City officials also have created a separate entity that accepts corporate money to fund events around the convention, including a welcoming party for journalists paid for by Time Warner Cable.

Some corporate help to the Democratic convention is known, but only because of the companies themselves. Officials from several of the corporations funding the Republican event have said the companies also would provide services to the Democrats. AT&T announced that it was the official “wireless and mobility provider” to the Democratic convention, bringing in temporary cell towers and other services. And Coca-Cola, the “official recycler” of the GOP convention, said it would also help the Democratic convention.