In its announcement about earnings, Warner said that earnings this year would be 10 percent to 15 percent greater than those of 1981 - significantly below previous expectations. It also said fourthquarter earnings will be below the $75.84 million, or $1.17 a share, recorded in the fourth quarter of 1981.

For all of 1981, Warner earned $226.5 million, or $3.57 a share, on revenue of $3.2 billion. Warner's Consumer Electronics Group, in which Atari is the major operation, accounted for more than half of Warner Communications' profits and revenues in this year's third quarter.

Based on Warner's statement, its earnings for 1982 are likely to be between $3.92 and $4.10 a share. That means that earnings for the fourth quarter will be between 46 cents and 64 cents a share, roughly half the level of last year's fourth quarter.

Atari said major factors in the decline for the quarter had been disappointing sales of game cartridges and substantially lower sales of coin-operated games for arcades. The company also said earnings were hurt by a one-time charge for the disposition of significant portions of the Knickerbocker Toy Company. Fears Spark Stock Swings

Warner's stock has been subject to steep price declines at various times during the past year because of fears that growth in the video game industry might be slowing. There have also been fears that a proliferation of suppliers, as well as competition from inexpensive home computers, would lead to great price competition and a shakeout in the video game business. Yesterday's announcement seemed to revive those fears.

In its announcement, Warner did say that despite disappointing figures, sales of game cartridges would be substantially higher than in 1981. It also said sales of its video game console system were running ahead of budgeted levels and would exceed 1981 sales.

James H. Levy, chairman and chief executive of Activision, which makes game cartridges that can be played on Atari's machines, said Atari's announcement reflected more about Atari's loss of market share than about the overall state of the video game industry. Competition Hurts Market Share