It was early on Sept. 11, 2001, and Robert C. Bonner, newly named but not yet confirmed to head the U.S. Customs Service, was at the Treasury Department receiving a briefing. Suddenly, the building was evacuated following news of the attacks in New York. Minutes later, speaking by secure phone with a top aide he had barely met, Bonner was told, "Sir, we need to declare a Level One Security Alert."

Bonner had one question: "Ahhh, what's a Level One Security Alert?"

He realized then that, whatever his inexperience at the agency, he now had the difficult job of refocusing the 22,000-employee agency toward a new mission -- stopping terrorists from penetrating U.S. borders.

Since that day, Bonner has received strong reviews for the grit and aggressiveness he has brought to the job, and also for his sensitivity to the needs of the U.S. business community, which fears obsession with security will choke off global trade.

Customs did shift to Level One security that day, and its inspectors at 301 ports of entry immediately ratcheted up scrutiny of incoming cars, trucks, trains and ships. Soon, lines at the bridges connecting Canada and Michigan stretched for miles, and waiting times grew to 12 hours.

U.S. car manufacturers, who would have to shutter their plants without Canadian parts, feared an economic catastrophe, and Bonner quickly learned the dangers of overcorrecting. He hurriedly lined up help from Canadian officials and the Michigan National Guard, and he had lines at the border back to normal within days.

"We have these two huge twin goals that we need to attend to, providing security and allowing for trade and travel," Bonner said in a recent interview.

"I give Bonner a lot of points," said Stephen E. Flynn, a former Coast Guard commander who directed an authoritative Council on Foreign Relations task force on domestic security last month that issued scathing criticisms of vulnerabilities at U.S. harbors. "He's done a great job" at the main tasks of a Customs commissioner in this crisis, Flynn said.

Instead, Flynn said, U.S. port security has been hobbled in part because Treasury Department and congressional officials failed to fully fund some security needs.

Bonner has earned a reputation for forcefulness throughout his career. As a U.S. attorney in Los Angeles in the 1980s, he prosecuted the Mexican murderers of kidnapped Drug Enforcement Administration agent Kiki Camarena, winning convictions against 10 men, including some Mexican officials.

Named DEA administrator in 1990, he immediately ordered his subordinates to make cases against big-time money launderers. For the first time, the U.S. government would stanch drug dealers' money flow. The DEA unit devoted to the task grew from two people to 80 almost overnight.

"He's all about taking action and changing things," said Gregory Passic, who ran that DEA team and now probes terrorist financing for the National Security Council. "He was one of the first guys to realize the importance of financial investigations."

Bonner aides point out the irony that this former DEA chief is now traveling the nation, urging Customs employees to end their single-minded pursuit of finding narcotics in people's luggage and to focus more on spotting enriched uranium and nuclear bombs.

FBI officials say Bonner has been overly ambitious in steering Customs into complex terrorism investigations, such as the probes of terror funding by its Operation Greenquest. Customs agents, the FBI officials say, are in over their heads in the realm of terrorism and lack the security clearances to do the job.

Bonner's defenders scoff at the criticism, saying that Customs has decades of experience attacking money laundering and that the FBI criticism is based on turf consciousness.

Bonner declined to respond. Passic explains why: "This is not a parochial guy."

Bonner again demonstrated his penchant for action weeks after the Sept. 11, 2001, attacks. Congress was passing a new law requiring foreign airlines to provide Customs with lists of arriving passengers. But the law wouldn't take effect for months, and some Middle Eastern airlines balked. So Bonner ordered that all passengers of uncooperative airlines be searched upon arrival.

"Within days, we had 100 percent compliance because he played hardball," a Bonner aide said. "We got a quick education who this guy is."

Much of Bonner's time has been devoted to enlisting 1,000 U.S. importers, shipping firms and other businesses in a counter-terrorism program of his design. They must perform employee background checks and take other steps to tighten security; in exchange, they receive expedited processing of goods across borders.

But his top priority has been intermodal containers, the 40-foot-long metal boxes that are loaded on ships, trains and trucks and handle 90 percent of the world's cargo. Customs inspectors can scrutinize only 2 percent of the millions of containers entering U.S. ports every year.

In an effort to, in Bonner's words, "extend the perimeter outward," he has traveled the world, persuading 14 of the world's top 20 ports -- from Rotterdam to Singapore -- to agree to new security procedures and allow Customs employees to inspect goods at their seaports. Their payoff, again, is faster processing of goods entering this country.

Trade experts express amazement at the speed with which Bonner has persuaded foreign trade ministries to join in -- and with minimal help from other U.S. agencies. Just two weeks ago, he got China's two mega-ports on board, and last week Italy's port of Genoa signed up.

Bonner has generated more controversy in ramming through his bureaucracy a new rule requiring importers to provide Customs with manifests of their incoming cargo 24 hours before the goods are loaded at a foreign port. Customs officials said they need such data to decide which containers should be scanned with high-tech machinery or searched.

Some trade firms, especially Customs brokers, protested, saying the rule would require too much paperwork and cost them money. Bonner granted a few concessions -- exempting bulk importers of oil and lumber, for example -- but essentially stuck to his plan.

"I don't know if I'd say it was quite ramming down our throat," said Federico C. Zuniga, president of the National Customs Brokers and Forwarders Association, "but they had a set plan and they followed it."

Robert C. Bonner has been praised for his forcefulness as Customs Service commissioner since Sept. 11, 2001. He ignited some controversy by requiring importers to submit cargo lists 24 hours before loading at foreign ports.