A bidder in the battle for the District's cable television franchise filed a $125.7 million antitrust lawsuit in U.S. District Court yesterday, contending that the winning firm and its business partner, the C&P Telephone Co., conspired illegally to win the exclusive city cable contract.

The lawsuit, filed by Capital City Cable, seeks an injunction to block a recently negotiated agreement between the D.C. government and District Cablevision Inc., which had been expected to gain final approval from the City Council next month.

Named as defendants in the suit are District Cablevision, C&P, the District government, the City Council and its individual members, Mayor Marion Barry, D.C. cable director Richard Maulsby and Elijah B. Rogers, a former Barry aide.

The council granted tentative approval in July to District Cablevision to provide a 79-channel cable system for the District within four years. It was unclear yesterday what impact an injunction, if granted, might have on company plans to offer stock to outside investors as part of its financing strategy.

District Cablevision President Robert Johnson said he had not seen the lawsuit and declined to comment.

Capital City Cable alleged in its complaint that C&P illegally attempted, with the help of Barry and Rogers, to influence all three original bidders for the franchise to grant a role to the telephone company in building and maintaining the District's cable system.

After District Cablevision agreed to take on C&P as a partner in the venture, the lawsuit charged, District officials conspired "to eliminate competitors by providing preferential treatment" to District Cablevision's bid.

The complaint alleges that C&P's involvement in the city's cable system, including separate lines for data transmissions by local businesses, would give the company "predatory, monopolistic and anticompetitive control" over telecommunications in the District.

C&P spokesman Web Chamberlain said the company will have no comment until officials have studied the complaint.

Capital City Cable and the City Council's cable subcommittee both have asked the Justice Department to investigate C&P's role in the venture. C&P also needs the approval of the Federal Communications Commission before embarking on cable construction.

Capital City Cable alleged that members of an advisory cable design commission met in an illegal, private meeting in May at the home of one of the members "to promote and orchestrate a favorable vote for the District Cablevision/C&P bid at the next day's official Design Commission meeting."

The next day, according to the complaint, the commission voted to recommend District Cablevision's proposal to the council, although a city-paid consultant had ranked Capital City Cable first among the three bidders.

William Lightfoot, chairman of the 28-member commission, said yesterday that the private meeting involved between four and seven members and did not represent a quorum.