At 5 p.m. Thursday, acting CIA Director John E. McLaughlin, in his other capacity as acting director of central intelligence, conducted the daily counterterrorism meeting where the first information about the latest detailed al Qaeda threats was discussed among senior CIA, FBI and military officials. They set in motion plans for antiterrorism operations in the United States and overseas, ultimately leading to yesterday's announcement of an elevated terrorism threat more specific than any the government had ever issued.

Surrounding McLaughlin were officers who once were prohibited by law or habit from working together: CIA operatives from the clandestine service who work today at the agency's Counterterrorism Center and its Terrorist Threat Integration Center; FBI agents; representatives from the National Security Agency, which intercepts communications around the world; analysts from the Defense Intelligence Agency; and senior military officers who help the CIA execute or coordinate foreign operations.

Once considered as separate as church and state in the United States, these agencies have worked together for more than two years, meeting daily at 5 p.m. in response to the missed opportunities recognized after the Sept. 11, 2001, terrorist attacks.

"Sunday's action is a classic example of how fusion [in intelligence operations] now works in the post-9/11 environment," a former senior intelligence official said yesterday.

The agencies' cooperation on planning counterterrorism activities has not been previously highlighted. Before the developments last week that led to Homeland Security Secretary Tom Ridge's announcement yesterday elevating the terror alert for the financial sector and specific buildings in Washington, New York and New Jersey, this cooperation by the FBI, CIA, NSA, DIA and military had led to the arrest of Jose Padilla in May 2002 at Chicago's O'Hare International Airport for allegedly plotting possible attacks in the United States with al Qaeda.

Although federal law prevents the CIA from carrying out operations within the United States, nothing bars it from discussing plans for domestic activities with the FBI, and recent changes in the law permit more open sharing of information. For example, CIA officers are stationed at many of the FBI's joint terrorism task force centers in cities across the country.

"There is no ban on talking jointly," said a senior counterterrorism official, citing the case of someone the CIA has been surveilling overseas who arrived in the United States. "The FBI takes the lead but has CIA support in this country," he said, speaking with the understanding he would not be named.

Even before Ridge's announcement yesterday, CIA officials had agreed Friday to make the senior counterterrorism official available to discuss the 5 p.m. meetings and interagency cooperation for the first time because they were frustrated that the Sept. 11 commission and the public may force a radical change in the system without taking time to understand what already is occurring. The officials said that changes more modest than moving the operation under the direct control of the president, as the commission has urged, could be sufficient.

The commission wants to replace the current system by establishing a national counterterrorism center within the Executive Office of the President. The center would report to a new national intelligence director, also inside the White House. The bipartisan commission, based on its study of the 2001 terrorist attacks and their aftermath, concluded that the system in place then did not work and required establishment of a separate counterterrorism center.

As commission Vice Chairman Lee H. Hamilton explained at Friday's hearing before the Senate Governmental Affairs Committee: "One of our principal feelings is that in dealing with counterterrorism, you must get away from -- this division of foreign intelligence is over here and domestic intelligence is over here and never the twain shall meet. That's a prescription for disaster, we think."

Asked about Hamilton's statement, the senior counterterrorism official said, "We keep looking at how to keep expanding this interagency program" being run by the director of central intelligence.

"A lot of the intelligence war involves people overseas and in the U.S. and requires cooperation across the government," the official said. "There are five or six around the table briefing on the war, sometimes involving a tactical operation here or in country X against an al Qaeda operative to take him down."

"The 5 o'clock meeting has an operational focus," said one former senior intelligence official familiar with the sessions. "There is full transparency with information shared across the table."

One irony of the commission's proposal is that it sees the CIA-established Terrorist Threat Integration Center as the starting point for its new national counterterrorism center, but it would use CIA and FBI analysts and operational personnel already involved with the CIA-run Counterterrorism Center. Even before the commission's recommendations were formulated, plans were being carried out to bring together the Threat Integration Center, the CIA's Counterterrorism Center and elements from the FBI's counterterrorism center in the same Northern Virginia building.

The Senate Governmental Affairs Committee will have an opportunity to explore the 5 o'clock group's activities at a hearing Tuesday, when witnesses from the CIA's two antiterrorism centers and the FBI are scheduled to testify.

A second purpose of the daily 5 p.m. multi-agency session is to prepare McLaughlin, again in his role as acting director of central intelligence, for meeting the next morning with President Bush. Sometimes the 5 o'clock group concludes that the president needs to talk to a foreign leader to provide sensitive aid on a case or take some other action at a senior level. When Bush is in Washington, the morning meeting provides an opportunity to share plans with Ridge and FBI Director Robert S. Mueller III, who both normally attend the Oval Office session.

The current purpose of the 5 p.m. meeting "is light-years different than it was . . . years ago" when "it involved military planning versus the Taliban," the counterterrorism official said. After the Sept. 11 attacks, "it evolved more into the global war on terrorism, foreign relationships with U.S. dimensions pushing data to the FBI and now even assurance that Homeland Security gets and passes information out locally."

"But despite some problems over timing and information sharing, I think the reason the [terrorist] war has remained offshore is due to disruptions we have caused," he said. "Now it seems a success, but only against three years ago."

Staff writer Dana Priest contributed to this report.

CIA head John E. McLaughlin chairs a daily meeting on counterterrorism.