The debate over open access for cable-modem service in American homes turned technical yesterday, as a senior official at AT&T Corp.'s high-speed Internet service questioned whether an open system that GTE Corp. recently tested in Florida really worked as described.

At Home Corp.'s chief technology officer, Milo Medin, suggested at a news conference that there might be political motives behind GTE's announcement Monday in Washington that it has low-cost technology that allows multiple Internet service providers to use the wires of a single cable TV system.

The purpose may have been to "incite municipalities to do what Portland did," Medin said. Recently a federal district court in Oregon ruled that the city had authority to mandate cable companies provide open access to Internet providers to offer service over cable networks, which are being upgraded as high-speed Internet conduits into millions of American homes.

At Home, an affiliate of AT&T, has argued that technology that would allow this kind of open access would require enormous investments of time and money. But GTE's trial in Clearwater, Fla., completed a month ago, claims to show the contrary.

As AT&T embarks on a multibillion-dollar acquisition spree of cable systems, Internet companies have expressed concern that they will not be able to use the company's lines to reach customers.

GTE's trial has serious flaws, At Home officials said. Medin pointed specifically to the lack of explanation from GTE on how it plans to allocate cable capacity fairly among multiple Internet service providers to prevent them from "clobbering" one another. The number of participants in GTE's trial was also not significant enough to prove the technology is feasible on a much larger scale, he said.

GTE officials responded that the technical questions that At Home officials raise are misleading. What At Home is saying "has nothing to do with equal access," said Al Parisian, who oversees GTE's business development in broadband services.