WASHINGTON — Advocates of a bill promoting openness in government are fuming that a Republican senator is blocking a vote.

Dozens of journalism and advocacy groups supporting the Open Government Act argue it would speed up the government’s response to public requests for information under the federal Freedom of Information law.

Senator Kyl, a Republican of Arizona, says the Justice Department is concerned that it could force them to disclose sensitive information.

In a statement yesterday, Mr. Kyl said the agency’s “uncharacteristically strong” opposition is reason enough to think twice about the legislation, and he will block a vote until both sides can work out the differences.

Advocates who range from the Society of Professional Journalists to the Humane Society of the United States are especially frustrated because Mr. Kyl had objected under a Senate rule that allows members to hold legislation anonymously.

Mr. Kyl disclosed his name yesterday, days after the bill’s backers launched an e-mail and telephone campaign, urging their supporters to help in “smoking out ‘Senator Secrecy.'”

They pointed out the irony that an open government bill was being blocked using a rule that allowed secrecy.

Supporters say the bill would plug loopholes in the FOIA law.