Three weeks ago, Secretary of State Condoleezza Rice held a news conference announcing broad changes to the department's arms control and nonproliferation bureaus. The first office had lost significant responsibilities during President Bush's first term as the White House pulled out of several international arms treaties. At the same time, the nonproliferation bureau's responsibilities tripled as officials handled crises with Iran, North Korea and a nuclear black market run out of Pakistan.

The bureaus had been under the control of John R. Bolton, who was about to be appointed ambassador to the United Nations after an unsuccessful confirmation process. With his departure, Rice said the bureaus would be merged into the newly named Bureau for International Security and Nonproliferation with a revised mission to address concerns such as the nexus between terrorism and weapons of mass destruction.

But the restructuring, expected to begin this week, has been put on hold by Rep. Henry J. Hyde (R-Ill.), the powerful chairman of the House International Relations Committee, counterparts on the Senate Foreign Relations Committee and State Department officials confirmed yesterday.

Hyde's spokesman, Sam Stratman, said the hold "reflects a desire for more specific information, which we have every reason to believe will be forthcoming."

The State Department notified Congress of the plans Aug. 1, the first day of August recess, and had sought approval by Aug. 15, weeks before Congress returned and had an opportunity to explore the merger.

"No one should be surprised that in this kind of last-second approach, people will want to slow down and take a look at what this all means," said Norman Kurz, spokesman for Sen. Joseph R. Biden Jr. (Del.), the Senate Foreign Relations Committee's senior Democrat. "Even if this ends up being the right course, the senior members of the relevant committees want to make sure that it makes sense," Kurz said.

On Monday, Bolton's chief of staff at State, Fred Fleitz, briefed staff members on the Senate committee about the merger. Many of the details and structural changes were worked out in private by a small group of political appointees who worked for Bolton.

Fleitz was questioned by the same Senate committee staff several months ago in connection with Bolton's contentious nomination. At Monday's briefing, he was joined by Stephen G. Rademaker, who since 2002 has been assistant secretary of state for the now-vanishing Bureau of Arms Control.

Despite the heavy workload, the other disappearing bureau -- for nonproliferation -- has been without an assistant secretary for more than a year, since John S. Wolf left the administration in June 2004.

Rademaker, who is close to Bolton, has been overseeing the nonproliferation side but has not been formally appointed assistant secretary for that bureau or the new one. Officials said there were unresolved questions about whether Rademaker would need to be reconfirmed if he is named to run the joint bureau. The State Department has been trying to make a legal case to the congressional committees that a second confirmation is unnecessary. But some Senate members are pushing for hearings.

The new bureau will report to Robert G. Joseph, who in May replaced Bolton as undersecretary of state for arms control and international security. Joseph handled similar issues at the National Security Council during Bush's first term, and there had been speculation that he may want the new post filled by a White House colleague.