Cable News Network, the 24-hour-a-day all-news venture of Atlanta television and sports magnate Ted Turner, will show a profit within a year despite currently losing $1 million a month, Turner told an industry convention last week.

At the same time, Turner also used the Western Cable Show to announce that his company, Turner Broadcasting System, would launch early next year its third cable programming service -- a 24-hour voice-and-text program that will provide up-to-the-minute listings of cable programming across the country.

In a speech mixed with plaudits for cable system operators and barbs directed at the nation's three over-the-air television networks, Turner told a cheering breakfast crowd that Cable News Network, which now serves 4.2 million homes, would reach 10 million to 11 million homes within a year.

In addition, officials of Turner Broadcasting said the company has now lined up 70 advertisers for the round-the-clock news service and in November recorded $1 million in advertising sales -- the largest month since the news service began operation in June.

Turner also cited recent Nielsen figures which indicated that in 53 percent of the homes with Cable News Network the service is watched at least two hours a day -- the strongest suggestion yet that the service is headed for a rosy future.

Turner also said that, of the homes surveyed that rely of television as their primary news source, Cable News Network is the favorite news offering for more than 33 percent of the viewers, trailing only American Broadcasting Co. Inc. among the major networks and by only 6 percentage points.

The outspoken owner of the company, which also operates Channel 17 of Atlanta, a UHF station beamed via satellite to cable homes across the country, also used the forum as another platform for what has become a series of increasingly bitter attacks on the major networks.

Noting that both ABC and Columbia Broadcasting System are vigorously marketing cultural programming networks for cable operators at this convention, Turner accused the networks of giving the public a "diet of disasters, scandal and sleazy sex. t

"Two of the three networks are here trying to get you to affiliate with them even though their public stance to the business press is still offensively anti-cable," Turner said. "They're here because they're beaten."

Turner whose marketing of Channel 17 is widely credited with playing a vital role in the current cable boom, also predicted that cable television will reach 90 percent to 100 percent of the nation's homes by 1990 and that the product eventually would change newspapers dramatically from the way they are delivered today.

"What you want to do is supplant as much information that comes in the mail as possible," Turner told a wildly enthusiastic audience of close to 1,000 people. "And it's going to work."

The new service announced by the Turner company last week will provide continuing one-minute summaries of future programming offered by cable systems nationwide, while leaving open time for cable operators to list the programs available on the particular local system.