Hatch, chairman of the Senate Judiciary Committee, told the Progress and Freedom Foundation that many worry that "Microsoft is out to achieve, in effect, a proprietary Internet."
Microsoft has already had sanctions for what the government said was unfairly marketing its Internet Explorer by including it free in its Windows software (that operates most of the world's personal computers) - making access hard for competitors such as Netscape.
Hatch said if Microsoft eventually achieves a monopoly in Inter-net browsers and technology, "Rest assured that we will be hearing calls from all corners for a heavy hand of government regulation - for a new `Internet Commerce Commission.' "
Hatch added, "It seems far better to have antitrust enforcement today than heavy-handed regulation of the Internet tomorrow."
Hatch said, however, he would not try to strike down any monopoly created by market choice under fair competition.
But he said new technology-shifting products should have a legitimate chance to compete fairly in the market and not be killed in the crib by anticompetitive efforts blocking their access - and officials should ask if that is happening.
"I believe this is precisely the question - or one of the questions - presented by Microsoft today and is one of the reasons why Microsoft in particular inescapably invites scrutiny in the course of assessing competition policy in this digital age," Hatch said.
He added "one can hardly question" that Microsoft aims to dominate the Internet because of such actions as buying WebTV and its technology, "seeking to control Web software programming and tools markets with proprietary products" and through other "browser wars" between Microsoft's ActiveX and Sun's Java.
Hatch noted, however, that monopolies sometimes created by robust competition aren't always bad.
He said Microsoft's virtual monopoly in another area - operation programming for personal computers - brought benefit by creating a world standard to which other software developers write programming.
He said avoiding costs of trying to make programs compatible with many standards led to a "recent boom in software applications and the software industry generally."
Hatch said he plans to have his committee give scrutiny in coming months to how to identify when new technology is being unfairly blocked from the market, and whether current laws allow enforcers and courts to discover that in a timely fashion.