A sharply divided Federal Communications Commission left standing rules that require the four regional Bell companies to lease their networks to rival companies to provide local phone service to consumers.

In an extensive overhaul of phone regulation, the FCC did away with some requirements that affect competitive phone service for business customers.

It also did away with provisions governing high-speed Internet access, eliminating the requirements that force the Bells -- BellSouth, Verizon Communications, SBC Communications and Qwest Communications -- to provide rival firms discounts to lease fiber-optic lines to provide broadband service.

Critics say such measures could mean less competition, higher prices and less innovation down the road as new Internet services and technologies are rolled out.

''The FCC vote closes the door on the prospects for competitive Internet service providers in the broadband world,'' said Susan Ashdown, executive director of the American ISP Association, a Washington, D.C.-based trade association.

For South Florida, that means in areas where BellSouth has laid fiber-optic cable, such as the newer developments in West Broward and Miami-Dade counties, a rival firm wouldn't have access to its network to provide DSL service.

A few hours after the agency's ruling was handed down, some critics already had zeroed in on areas that could be challenged in court.

The broadband rule changes looks to be one area ripe for rival companies to take to court.

Consumers and businesses would be left with BellSouth or their cable company as their only choices for high-speed Internet access.

''It's a very monumental ruling,'' said Allison Hift, chairwoman of the telecom law group at Becker & Poliakoff, a South Florida law firm.

The FCC ruling, she noted, differentiates between the business and residential phone customers for the first time. It also sets different requirements on network access for providing voice phone services and more advanced services such as faster Internet access.

Hift said it seems as if the FCC has concluded there is enough competition in the market for business phone service, and noted that the new FCC provisions would no longer require that the Bell companies to lease their switches to rivals.

A switch is a basic element of the nation's telephone network -- it connects one line to another. However, it's an expensive piece of equipment, usually coming with a seven-digit price tag.

For firms like Allegiance Telecom, which owns its network and switches to provide service to business customers in South Florida and more than 30 other metro areas around the country, Thursday's FCC decision has no impact, said L.C. Baird, vice president and general manager for the company's Miami office.

Allegiance, based in Dallas, only has to lease the ''last mile'' from BellSouth, the short piece of copper wire that runs from the central office to each business customer.

Yet, for independent carriers that don't own their switches like Allegiance does, the ability to service business customers could be curtailed.

Carriers such as Allegiance, or Orlando-based Florida Digital Network, are seen as the true competitors in the telecom world by many regulators and industry experts.

One key proponent is Michael Powell, the FCC chairman.

Powell was advocating a complete elimination of all the provisions that allow rival companies to have access to pieces of the Bells' network to provide local phone service.

Powell found support for his position from only one other FCC commissioner: fellow Republican Kathleen Q. Abernathy.

Powell issued a partial dissent on the decision, a rare move for an FCC commissioner.

The split decision ''created a Picasso-esque regulatory backdrop,'' Powell said.

Kevin J. Martin, another Republican commissioner, voted with the two Democrats on the board, Jonathan S. Adelstein and Michael J. Copps.

The Bell companies would have liked to seen Powell prevail on these changes.

''The FCC missed an historic opportunity to address serious problems in the vital telecommunications industry sector, with consequences for every American consumer,'' said Duane Ackerman, chairman and CEO of Atlanta-based BellSouth.

Major long-distance providers such as AT&T and WorldCom, who benefit from the rules that allow access to the Bells' network so they can provide local service, were generally pleased with the split decision.

The FCC ruling did allow the states to continue to monitor the spread of local phone competition, a position that the Florida Public Service Commission, like many other regulators, had advocated.

In the past 18 months or so, state regulators have been aggressively demanding the Bell companies lower the prices they charge for access to their networks in an effort to foster competition.

Consumer advocates were highly critical of the FCC decision.

''The FCC's action today is highly ironic. The rules the commission adopted preserve competition for 20th century technology, while ensuring monopoly for 21st century technologies,'' said Mark Cooper, director of research for the Consumer Federation of America.