That one-liner is vintage Klein -- off-the-cuff, slightly self-deprecating and yet shrewdly casting himself as the little guy taking on the business giant.

At an annual salary of $115,700, Klein may make a fraction of what America's richest man earns but he could end up being Gates' worst nightmare.

It was just a year ago that some US lawmakers criticised US assistant attorney general Klein as too weak to hold the critical job of chief US trustbuster.

In recent weeks, however, Klein has engineered the rejection of key mergers in the defense and communications industries.

And methodically, Klein has compiled one of the boldest US government antitrust challenges in history against Microsoft.

No one is calling Klein weak any longer.

Democratic president Bill Clinton said on Monday he had confidence in the way the justice department was handlingthe case. And in Congress, Klein has many fans among the majority Republicans. Senate judiciary committee chairman Orrin Hatch calls him one of the top legal minds in Washington.

Klein, 51, has risen from the son of a New York postal worker to holding the job of assistant attorney general in charge of the antitrust division. The antitrust division, along with the Federal Trade Commission, enforces the nation's competition laws.

He presides over one of the busiest bureaucracies in Washington. Amid a wave of corporate mergers, the justice department and FTC may look at some 1,000 cases this year. It will give close scrutiny to an unprecedented range of cases in dozens of business sectors.

But the Microsoft case is the crown jewel.

The powerful company has vowed to fight in court and critics are charging the government with acting like big brother, meddling in the economy.

Some critics believe the government risks getting mired in a legal morass like the disastrous case against computer giant IBM,which was dropped in 1982 after a 13-year fight.

Klein seems to take it all in his stride. A graduate of Harvard Law School, he was a law clerk for Supreme Court justice Lewis Powell, which turned out to be profoundly important in shaping his views.

In a recent interview with Reuters, Klein spoke at length about the values Powell espoused.

"His grounding was in reality, in practicality, in an understanding of institutions as well as individuals," said Klein. "He was not by instinct or nature an ideological or doctrinal person."

After Clinton's election in 1992, Klein worked at the White House as a deputy legal counsel and eventually moved over as second-in-command at the antitrust division.