The Alexandria Cablevision Co. expects to begin stringing cable for its 220-mile system within the next week or so, pushing closer to the day this fall when city residents can watch news, sports and other entertainment features around the clock.

Sue Cieslak, director of marketing and public relations for the company, said this week that approximately 50 miles of the system will be operational in October, allowing 15,000 residential units to hook up to the system.

Cable will continue to be strung at a rate of 20 miles a month until the projected goal of 55,000 households can be hooked up, Cieslak said. The system is expected to serve 45,000 households by the end of the 1981. The city's West End will be the first area to join the cable system because the "head end" -- the nucleus of the system where the antennas and electronic gear are located -- will be at the Fort Ward Towers apartment building on North Van Dorn Street.

The site was selected because its height is expected to provide the best reception, said Michele Evans, the assistant city manager overseeing the development of cable television in Alexandria.

The system will then stretch out along utility and telephone lines, above and below ground, to the eastern section of the city.

When completed, the Alexandria system will offer 35 channels in a "tiered" structure allowing subscribers to choose how much cable service they want.

At the first level, a subscriber will pay $9 a month to get all commercial stations in Washington, Baltimore and Northern Virginia, plus most of the added attractions that have made cable television so popular.

Among them are 24-hour news and sports channels, a children's programming channel, religious programming, a black entertainment network, coverage of the U.S. House of Representatives and the regular programming from round-the-clock "superstations" in Atlanta and New York.

In addition, there are four channels set aside for local use, such as coverage of City Council and school board meetings, and Colonial 10, a channel owned by the cable company which will be used for talk shows on issues of local interest.

There also would be channels providing weather reports, a consumer shopping guide and a community bulletin board.

The system eventually will have the capacity for two-way communication that will permit, for example, alarm hookups to the police and fire stations. Additionally, there will be channels that can be leased for personal and business-related reasons.

On the second tier, the subscriber would pay $18.95 a month to get all of the above plus a choice of Home Box Office or Showtime, basically recent-run movies and entertainment features such as nightclub acts. On the third tier, the subscriber would get the whole works -- both movie channels and all the rest -- for 24.95 a month.

Installation fees are expected to be waived in the first couple of months of operation to lure subscribers, Cieslak said.

Arlington is the only other metropolitan jurisdiction with cable television.

The system, which has been in operation since 1978, was installed by ARTEC. t