The alert came at 10:17 a.m. on a sultry summer morning on the Mississippi. A crop duster circled four times over the river near Natchez, Miss., sending clouds of dark powder down on the tugboat and barges below. The tugboat operator, alarmed, jotted down the plane's identifying numbers and called the Coast Guard: What was going on?

Within minutes, a Coast Guard supervisor in Baton Rouge, La., messaged the Homeland Security Operations Center in Washington, using a secure and encrypted network set up to report suspicious activity. Fearful of a possible chemical or biological attack, the center's director, retired Marine Brig. Gen. Matthew E. Broderick, called the White House Situation Room, then notified the FBI, the Transportation Department, the Department of Health and Human Services and several other agencies.

The crews on the boats were monitored for symptoms of poisoning, but none developed. Meanwhile, a deputy sheriff tracked down the pilot. It turned out that he had been drinking and doing drugs and was flying out of control. "We arrested him," Broderick said simply. "The guy was just a drunk."

It was another day, another false alarm for the nation's year-old Homeland Security Operations Center. In a brick complex five miles from downtown Washington, representatives from a multitude of agencies prepare for the day when a tip turns out to be real, signaling another terrorist attack on the United States.

Broderick has one major mission: Try to connect the dots in time to prevent catastrophe. One day last month, for the first time, he allowed a reporter to shadow him through a day.

Looking for Links

At 7:30 a.m., after a five-mile run around his Annandale neighborhood, Broderick arrived at a squat brick building near Ward Circle, across from American University in Northwest Washington. A no-nonsense Irishman from Worcester, Mass., with thinning red hair, a square jaw and solid build, he looks every bit the Marine he was for 30 years, including tours of duty in Vietnam and Somalia. Nowadays, he fights a different kind of war in a different kind of place.

As he strode to his office in the heavily guarded campus that houses the Homeland Security Department, he passed signs pointing to "Cryptologic Court" and "Intelligence Way," named during World War II, when Navy cryptologists working at the campus tried to break German codes. He stopped to deposit his cell phone in a locker at the entrance; no one is allowed to bring communications devices inside.

This morning, he learned in his first briefing of the day, agents were closely tracking three reports that a few years ago would not have solicited more than a raised eyebrow in Washington. Broderick quickly scanned them:

* In Miami, a man tried to board an airplane with a bizarre, handmade contraption, a vacuum cleaner hose taped to tin cans and air filters. Federal agents confiscated the hose, worried that it could be used as a lethal device. The man was stopped from boarding and was being questioned. Meanwhile, a digital photo of the device was being studied by a DHS engineer.

* Customs agents and Border Patrol officers were investigating a "tool" sold overseas -- Broderick would not be more specific -- that they feared could be used as a weapon.

* In a northeastern city that Broderick would not name, police and federal agents were working a tip that several empty suitcases had been left in bus terminals and other areas.

At the same time Broderick learned of those and other, classified, developments, one of his staff members was in the White House Situation Room briefing Homeland Security Secretary Tom Ridge, who in turn would brief President Bush on the most important items.

The center is critical to the government's efforts to address an issue raised by the National Commission on Terrorist Attacks Upon the United States: the failure of agencies to share information with one another. That problem has come under intense scrutiny since the Sept. 11, 2001, terrorist attacks.

All sides have vowed to change the culture, but some skeptics doubt that intelligence agencies will share their deepest secrets with one another. The director of the CIA, for example, oversees another multiple-agency command center set up a year ago by the president -- the Terrorist Threat Integration Center. But Broderick says the two aren't in competition: His center focuses on activities in the United States, while the other has a global mission.

Tomorrow, Ridge will have to address those issues before the Sept. 11 commission. Lawmakers have slammed his department as slow-moving, disorganized and undermanned. Private citizens have derided the department's color-coded threat levels and questioned the effectiveness of airport security checks. Rep. Harold Rogers (R-Ky.), chairman of the House Appropriations subcommittee on homeland security, has criticized its "turtle slow" pace in hiring intelligence analysts.

But last week, asked about the operations center, Rogers had nothing but praise. The center, he said, has already brought about "unprecedented sharing."

"This will take time, but we've left the starting block," said retired Marine Lt. Gen. Frank Libutti, now an undersecretary of homeland security.

'One-Stop Shopping'

Inside two long, narrow rooms, a CIA agent sits in front of a computer next to an FBI agent, who sits next to a National Security Agency official, who sits next to a Defense Intelligence Agency employee -- 28 representatives in all from local, state and federal agencies. They are identified by an alphabet soup of abbreviations hanging from the low ceiling: TSA, USCG, DEA, DOD, MPD, ATF. A favorite Broderick motto hangs in the hall outside: "Nothing is routine after 9/11."

This is the hub of Broderick's operation. Each day, the agents examine hundreds of pieces of intelligence e-mailed or called in from law enforcement officers across the country through the Homeland Security Information Network. The network is linked to 1,500 users in hundreds of agencies and certain businesses that could be terrorist targets -- airlines, nuclear power plants, chemical manufacturers. Eventually, it will hook up to 5,000 users across the country, including mayors and governors, for instant and secure communication.

The agents are constantly conferring with each other. Sometimes they fire off a message to police departments or health agencies, asking whether a particular type of incident has occurred elsewhere in the country. On the walls, giant screens display documents and maps (one shows the location of nuclear power plants) along with the 24-hour cable news channels, most on mute.

More than half of the information streaming into the operations center has to do with suspicious people trying to enter the country. Someone recently tried to get past U.S. customs with carry-on luggage containing a bag of powdered sugar with an alarm clock on top. After verifying the powder wasn't an illegal substance, customs agents let it through. "Was this a test of the system?" Broderick asked. "We can't get complacent," he said. "Nothing is too small to run down."

Almost every day, reports come in from the Transportation Security Administration about items that airline passengers try to take onboard. One man tried to hide a set of large butcher knives in his carry-on bag. (He turned out to be a chef worried that the airline would lose his knives.) Another man hid a pair of pruning shears behind a false side of his attache case.

Several people have been stopped carrying hollowed-out appliances. ("It's not illegal, but was someone rehearsing something?" Broderick asked.) Others have tried to board with loaded guns, which are confiscated. "They were in a state where they can carry a firearm and they say they forgot to take it off," Broderick said incredulously. "They're going through security, they have to take their shoes off and are going through a metal detector, but they forgot?"

Each time an incident unfolds, the center disperses the information to the proper agencies, monitors developments and canvasses for more information. "Without a doubt, this is one of the best things that has happened since 9/11," said Michael R. Bouchard, assistant director of the Bureau of Alcohol, Tobacco, Firearms and Explosives, which has two senior agents in the center.

"It's one-stop shopping," said U.S. Capitol Police Chief Terrance W. Gainer, who said Broderick called him shortly after ricin was discovered in a Senate office building in February and provided him with quick links to the Environmental Protection Agency, federal laboratories and the U.S. Coast Guard, which has expertise in hazardous-material cleanup. "It would have been tougher without the coordination of the Homeland Security Operations Center."

Preemptive Action

Broderick passes on eight to 10 pieces of information daily to the intelligence unit across the hall. "I don't do intelligence analysis," he said. "We're the guys down in the mine picking up these nuggets."

But sometimes circumstances demand immediate action. Broderick's operation triggered Homeland Security's first full-scale alert during last summer's power outage in New York. The center sent out warnings to law enforcement agencies and first responders across the country, and staff members monitored the situation for signs that the blackout was triggered by terrorists.

Last fall, the center made the decision to shut down 13 post offices in the Washington area when a powder that initially tested positive for anthrax was found at a mail facility at the Anacostia Naval Station. During Hurricane Isabel, it was in touch with all relevant agencies -- the Federal Emergency Management Agency, local leaders, the FBI, police -- in case anyone tried to take advantage of a vulnerable city. In February, the center issued an alert with the FBI about 9,000 blank French passports and 6,000 vehicle registration cards that had been stolen outside Paris. They messaged customs and immigration officials and anyone else they thought should be on the lookout for the documents.

This spring, the center sent a representative to San Antonio to check on security measures for the NCAA Final Four basketball games. And in the coming months, it is braced for "suspicious activity" tips around the Fourth of July holiday and the Democratic and Republican national conventions.

During the Code Orange heightened terrorism alert level in December, when dozens of flights to the United States were canceled, Broderick often worked 36 hours straight. Ridge would join him at 3 a.m. in the center for a sandwich.

"He was here at 4 and 5 in the morning," Broderick said. "It was very serious. There were threats to blow up airlines and the possibility of large numbers of American casualties." Broderick said he slept on the floor of his office several nights. (He has asked for a sofa in his new office upstairs. "The floor is very hard," he said, "and I'm an old Marine.") But recently things have been calmer, and by the end of this day, many of the morning's incidents have been resolved:

After several meetings and many phone calls, federal agents had notified all concerned parties to be alert to the device that they worried could be used as a weapon.

The search for empty suitcases turned out to be a bust. The tip that several empty suitcases had been found in one city was revealed to be based on bad information, and law enforcement officers did not find empty suitcases at bus terminals in any other cities.

Police and federal agents determined that the Miami man with the tin cans and hose was also not a threat. "It turns out the guy was a flake who just wanted his own air-cleaning device," Broderick said.

Tonight, it turned out, he would get a decent night's sleep.

Staff researcher Bobbye Pratt contributed to this report.

Matthew E. Broderick, standing at center, head of the Homeland Security Operations Center, confers with Cmdr. Malcolm Johns of the Public Health Service as the effort to avert disaster continues. The operations center is connected to hundreds of agencies by way of a secure and encrypted network.Personnel are required to put communication devices such as cell phones into locked boxes before entering the operations center.