Without fanfare or debate, the City Council voted yesterday to modify substantially its cable television franchise agreement with District Cablevision Inc. to help the financially troubled firm raise enough money to start building a cable system here by early next year.

The modifications were approved by 10 of the 11 council members attending yesterday's meeting, with only Carol Schwartz (R-At large) voting against the modifications.

The franchise changes will become law after they receive a second and final council vote, are approved by the mayor, and undergo a 30-day congressional review period. The council is scheduled to give final approval to the modifications Sept. 24.

Before that time, the council has stipulated, District Cablevision must sign the limited partnership agreement it negotiated with Tele-Communications Inc., the Denver-based cable operator that offered to put up $45 million in financing for the cable system.

As part of the modifications, the 15-year franchise agreement awarded to District Cablevision last February would be transferred to a limited partnership in which District Cablevision would have a 25 percent share and TCI a 75 percent share.

Betty Ann Kane (D-At Large), chairman of the council's cable committee, said that after months of bitter debate over the modifications the council is now confident that the city has a "workable" contract with District Cablevision.

She also said that transferring the franchise would allow the city to hold both District Cablevision and TCI liable if the franchise requirements are not met.

Robert L. Johnson, president of District Cablevision, said yesterday that TCI has agreed to the modifications approved by the council and that he does not anticipate any problems in getting TCI to sign a final agreement.

"We think both District Cablevision and the city have gotten a franchise that is economically viable to serve, to the maximum extent possible, residents of the District," Johnson said.

Under the construction schedule submitted to the council, District Cablevision would wire the entire city within five years. Johnson said yesterday that construction could begin as early as next February and that cable servies would be activated in some homes by next June or July.

Johnson and other District Cablevision officials had asked for franchise concessions worth millions of dollars after the company failed to obtain the necessary financing to build the cable system it proposed.

The modifications approved by the council would reduce the number of residential cable channels from 78 to 54, reduce the amount of original financial commitments to public and municipal programming, and delay the activation of an institutional cable network designed for use by businesses and institutions such as hospitals and schools.

During several months of debate on the issue, some council members objected to making the changes, saying that District Cablevision had substantially altered its original promises. But before entering yesterday's meeting, a number of the council members said privately that compared with modifying the franchise, the chief alternative -- starting the process all over again -- would delay even further the arrival of cable in the District.

Kane's committee had recommended that the modifications be approved, and without any debate the City Council did just that yesterday.

In other council action, H.R. Crawford (D-Ward 7) introduced a bill that would require the establishment of a residential health-care treatment facility for people who are suffering from acquired immune deficiency syndrome (AIDS) and require the mayor to develop within six months a comprehensive plan for treating AIDS.