Fairfax County supervisors yesterday again postponed a decision on whether to approve Cox Communication Inc.'s $1.4 billion purchase of the county's cable system, saying they want to seek more commitments from the company for improved service for the 244,000 customers.

By a vote of 7 to 3, the board delayed action on the sale of Media General Cable of Fairfax until Sept. 13. Several board members said they are increasingly frustrated by the refusal of Media General and Cox officials to offer guarantees about better converter boxes and more choices for customers.

"It's like the Lily Tomlin skit," said Supervisor Gerald E. Connolly (D-Providence). "We're the phone company. We don't care. We don't have to."

Yesterday's action was the third time the board has put off the cable vote to allow negotiation with Cox and Media General. Supervisor Stuart Mendelsohn (R-Dranesville) said the company has repeatedly refused to do anything but offer vague promises.

"They keep telling me all the things they are going to do," Mendelsohn said. "When I say put it in writing, they won't do it. We have a lot of unanswered questions that have been raised over the last several weeks."

Cox Vice President Claus Kroeger said after the meeting that he was disappointed by the board's vote. He said his company has agreed to spend $300 million to upgrade the Media General system. Cox officials have said that upgrade will be a huge benefit to the cable customers.

"I've never had this much trouble spending $300 million improving a cable system in my life," Kroeger said.

Federal law and county ordinance require Cox to get Fairfax's approval to buy Media General and take over the 15-year franchise agreement with the county, which ends in 2013.

Several supervisors have been critical of agreements between Media General and the owners of apartment buildings, hotels and businesses. Those building owners say the agreements prevent competition by locking them into long-term contracts with Media General.

Board members last week suggested forcing Cox to rewrite those agreements, a proposal that drew angry reactions from the cable companies. The county's attorneys warned supervisors that such an action probably would be illegal, but the issue is still on the table, supervisors said.

Yesterday, supervisors also raised a new issue, saying they want information about a nationwide fight between cable companies and Internet service providers. Several other local governments such as Portland, Ore., have attempted to stop similar purchases unless the cable company agrees to allow Internet providers other than the cable companies to provide high-speed access over the cable lines.

Regarding that issue, Kroeger said: "I'm a little puzzled that it hasn't been raised before 12 o'clock today. It's a non-issue."

He said that the approval process was being held up by the dispute over the apartment buildings and Internet access, not over the company's ability to provide quality service.

Three board members--Elaine N. McConnell (R-Springfield), Sharon S. Bulova (D-Braddock) and Michael R. Frey (R-Sully)--voted against another delay yesterday.

"We have a company with an excellent reputation," McConnell said. "I think we take chances of losing companies like that when we act this way."