The Alexandria City Council last night deferred the award of a lucrative cable television franchise after a consultant cited what he called "serious deficiencies" in the financial arrangements made by the firm the council selected last week.

After several hours of debate, the council decided to postpone until Friday a decision whether to give a franchise to Alexandria Cablevision Corp. to build a cable TV network. The franchise award to the firm had been expected last night.

The council also voted to require the company to come up with an additional $1 million in financing to meet "deficiencies" cited by the consultant, accountant Lee A. Bertman.

The council was also under pressure from the Alexandria Telecommunications Corp. (ALTEC), a firm that is competing with Alexandria Cablevision for the franchise. ALTEC, which is half owned by the company that runs the Washington area's only operating major cable TV franchise - in Arlongton - claimed that the council violated its own rules by accepting information from Alexandria Cablevision after a deadline had passed.

An official of Alexandria Cablevision defended the company's plans and said it is well financed. He took no position on the council's requirement for an additional $1 million.

Bertman told council members that Alexandria Cablevision's proposed $5.75 million financing was so deficient that it posted the potential for "default" if it were not amended.

Bertmen said the extra $1 million, including $500,000 cash, would guarantee that the firm would be able to place the special cable TV outlets in Alexandria's thousands of high-rise apartments.

Cable TV provides a wide variety of commercial and educational stations unavailable through ordinary antenna reception. Alexandria Cablevision has said it can begin hooking up individual television sets to its cable in 16 months and that a subscription would cost $17 a month.

The city's 15-year cable TV franchise could yield its holder hundreds of thousands of dollars each year in profits.

The last-minute reports, analyses and contract adjustments were criticized last night by council member Beverly Beidler (D). "It really puzzles me that we can get to this stage of the game" and began to revise the franchise plan, she said. "That is totally in contradiction to the original plan."

When Bertman advised the council "to look very carefully" at the firm's capital expenditures "to be assured that there is enough money to ensure the success of the system," he got a sharp reply from council member Robert L. Calhoun (R): "That's what we hired you to do . . .and not at the last moment, either."

Bertman said many of the documents he was analyzing were submitted to him only within the last few hours, although the company had been told to submit them a week ago.

Alexandria Cablevision, like other firms competing for the franchise, includes many prominent local figures among its officials. Among them are former Democratic House of Delegates Majority Leader James M. Thomson and former council member James W. Carroll.

City Attorney Cyril D. Calley told the council last night it acted properly in permitting the firm to submit additional information. Calley was responding to complaints by Waller Dudley, attorney for the rival ALTEC firm.

The vote to defer the cable TV issue until Friday was unanimous. The vote to require Alexandria Cablevision to come up with the additional $1 million was 5 to 2, with council members Beidler and Ellen I. Pickering (I) voting no.