Federal Communications Commission chairman Kevin Martin on Friday blasted Comcast Corp.’s Internet practices and said the agency’s enforcement order against the company would protect consumers and competitors.

The controversial order was approved by a 3-to-2 vote, with the two Democratic members joining Martin, a Republican appointed by President Bush.

Comcast’s interference with traffic in its high-speed Internet service was more widespread than the Philadelphia company had admitted to, Martin said, forcing him to act.

The enforcement action was hailed as a landmark victory by “net neutrality’’ advocates for extending FCC authority to the Internet, but it was criticized by top Republicans and Comcast as too regulatory.

The company’s Internet-management practices amounted to opening private letters and reading them, Martin said. In this case, the letters were electronic packets of data traveling between computers on the Internet. Comcast said the comparison mischaracterized what it does.

As expected, the FCC ordered Comcast to give the agency more details of its “discriminatory’’ practices managing Internet traffic, submit a plan on how it intends to stop the practice by the end of 2008, and disclose the new practices to customers. The company has 30 days to comply. No fine was levied.

“Today’s action by the FCC may actually result in slower online speeds for 95 percent of America’s Internet consumers,’’ McDowell said. “Although I have a tremendous amount of respect for each of my colleagues, none of us has an engineering degree.’’

House Republican leader John Boehner of Ohio said the FCC enforcement was a “dangerous path’’ and one that could stifle innovation and “kill American jobs.’’

Comcast fiercely opposed the measure and said the federal agency was punishing it for breaking unspecified rules.

The company said it was considering “all our legal options’’ and was “disappointed that the commission rejected our attempts to settle.’’

Comcast’s allies said they believed Martin was motivated by his dislike of the giant cable TV, broadband and telephone company. Comcast and Martin have clashed over indecency on cable channels.

Tom Tauke, executive vice president at Verizon Communications Inc., said Verizon was not making a judgment on this “unique Comcast case.’’

But “with both the FCC and the Federal Trade Commission engaged in oversight of Internet usage and practices, new legislation and more regulation, with all their unintended consequences, are not needed,’’ he said.