He was vilified in U.S. industry and government circles for blocking the merger of General Electric Co. and Honeywell International Inc. in 2001 after the Justice Department had approved it. And when the European Union directorate he heads ordered Microsoft Corp. to remove a key feature from its Windows operating system, the U.S. antitrust community convulsed again.

Now, as Mario Monti ends a sometimes tempestuous five-year run as Europe's antitrust commissioner, the man known as Super Mario envisions a continuing need for regulators to tackle unresolved international antitrust issues that might put some in the United States on edge.

In a wide-ranging interview yesterday, Monti said E.U. competition policy is "now something to be reckoned with." He said he is confident that his likely successor, Neelie Kroes, who is awaiting confirmation, is a strong advocate who can continue to push in new areas if she chooses.

Monti said he is concerned, for example, that a U.S. state is free to subsidize companies -- often as inducement to locate in the state -- while nations in the European Union are prevented from doing so. He said the international community needs to find a common approach to subsidies.

He also questioned whether companies should be allowed to cooperate on setting prices on products they export to other countries. Currently, such "export cartel" activity is exempt from U.S. antitrust laws, because, Monti said, the action does not hurt U.S. consumers.

Monti suggested that governments should not be able to act as cartels any more than companies. The Organization of the Petroleum Exporting Countries, for example, has been able to set world oil prices and stay outside the reach of antitrust enforcement because the group is made up of governments, not companies.

"These are important issues in antitrust for the next 20 years," said Monti, an Italian economist.

As antitrust commissioner, Monti often was attacked by his critics as a power-hungry academic who knew little of corporate needs. Those who believe that markets should be unrestrained by regulation felt his primary motivation was to make the E.U. a gatekeeper on the world business stage, regardless of its impact on consumers.

But others credit Monti with bringing Europe's antitrust laws more closely in line with those in the United States, even if the Americans did not see eye-to-eye with him on every decision.

"He has brought economics to the fore," said Ernest Gellhorn, a professor of antitrust law at George Mason University. "I may not agree with all of his analysis, but he . . . invigorated antitrust enforcement. I'm an admirer."

Edward T. Swaine, a law professor at the University of Pennsylvania's Wharton school, said Monti was able to push through widespread reforms within Europe, often in the face of stiff resistance from entrenched bureaucracies in the E.U.'s member countries.

"He's made great strides in rationalizing the exertion of antitrust authority across Europe," Swaine said.

For U.S. authorities, perhaps Monti's greatest achievement has been to bridge, though not entirely close, a gap in how much to weigh consumer welfare in evaluating mergers and antitrust enforcement by pushing the E.U. closer to the U.S. view.

Antitrust philosophy in the United States holds that two players combining into a large entity can sometimes result in more efficiency and lower prices. European doctrine traditionally considered fewer players to be a recipe for higher prices over time, and the E.U. continues to be wary of dominant players' ability to use their power to muscle into other markets.

Nonetheless, Monti's views can often be counted on to ignite controversy. Gellhorn said he was puzzled by Monti's assertion that E.U. states are constrained from subsidizing their own companies, arguing that it happens all the time.

And Gellhorn questioned whether export cartels -- employed in industries such as heavy machinery -- have had a significant economic impact anywhere.

Daniel J. Gifford, an antitrust law professor at the University of Minnesota, said his study of E.U. merger cases found that the Europeans "use the American language of consumer welfare, but I think they mean rivalry for the sake of rivalry," preferring to preserve as many competitors as possible.

"There are a number of E.U. decisions where [it] is disapproving mergers that would have resulted in lower prices for consumers," Gifford said.

Monti and his staff, in fact, suffered a series of setbacks in the past two years at the hands of E.U. courts, which have overturned the regulators' decisions to block mergers of European companies.

The criticism he has stirred in the United States is nothing compared with the attacks Monti said he has received in some quarters in Europe, where countries have traditionally supported their own companies at the expense of competition.

He also chided the media for portraying him as an all-powerful decision-maker. In the case of Microsoft, he said, all 15 member countries supported the order that the company offer a version of Windows without its media player, and pay the biggest antitrust fine in history, roughly $600 million. The company is appealing the E.U. ruling.

Monti said that he could have imposed an order that would have applied worldwide, but he chose to defer to the wishes of the U.S. Justice Department that it apply only to Europe.

Mario Monti says E.U. antitrust policy is "now something to be reckoned with," as he steps down as commissioner. Mario Monti, an Italian economist, has many admirers, even among critics of his decisions as the E.U.'s competition commissioner.