CBS Inc. said yesterday that its after-tax earnings grew 53 percent in the fourth quarter of 1985 from the year before, but net income for the year declined 87 percent.

At the same time, Warner Communications Inc. reported profits for 1985 in contrast to losses in 1984, Brunswick Corp. reported higher earnings for the year and the quarter, Goodyear Tire and Rubber Co. said its earnings for 1985 were about the same as the year before and Western Union Corp. said it will post a large loss for the year.

In the fourth quarter, CBS had after-tax earnings of $55.4 million ($2.23 a share) on revenue of $1.35 billion. Net earnings came to $36.1 million ($1.22) on revenue of $1.33 billion in the final three months of 1984.

After-tax profits declined to $27.4 million (81 cents) in 1985, and revenue totaled $4.76 billion. That was down from 1984, when net income was $212.4 million ($7.15) and revenue were $4.64 billion.

CBS' 1985 financial performance was marred by the large amount of debt it took on in fighting off a hostile $5.41 billion takeover bid from Atlanta broadcaster Ted Turner. CBS's defensive strategy included buying back 21 percent of its stock for more than $1 billion.

Since that successful antitakeover effort, CBS has been selling assets to retire debt. The company also has been streamlining operations. Much of the decline in 1985 net income was due to the discontinuance in the third quarter of CBS's toy, theatrical film and home-computer-software businesses, the company said.

*Entertainment and communications giant Warner Communications Inc. yesterday posted profits of $111.2 million ($1.64 a share) for the fourth quarter and $195.3 million ($2.87) for all of 1985 in contrast with losses for all of 1984 and the final three months of that year.

The fourth-quarter profit included an after-tax gain of $86 million from the sale of Warner's interest in two cable television channels, Showtime-The Movie Channel and MTV Networks Inc. A year ago, Warner reported a net loss of $203.7 million in the fourth quarter which included a $225 million loss from discontinued operations. Revenue for the quarter rose 20.4 percent to $644 million from $535.4 million a year earlier.

For the year, Warner's profits included an after-tax gain of $94.2 million on the sale of the interests in Showtime and MTV as well as the sale of a portion of its interest in Hasbro Inc. Revenue rose 10.4 percent to $2.23 billion from $2.02 billion in 1984.

Warner's filmed entertainment division posted operating income for the year of $160.2 million on record revenue of $1.2 billion; the recorded music division posted operating income for the year of $112.7 million on revenue of $912.3 million, both new highs, and the broadcast and cable division, which includes results from Warner Amex, had profits for the year of $6.3 million in contrast with a loss of $51.6 million in 1984.

*Brunswick Corp. reported that net earnings increased 16 percent to $22.9 million (54 cents a share) for the fourth quarter. Net sales were $388.6 million, a 12 percent increase from the same period in 1984.

For the year, net earnings increased 6 percent to $110.3 million ($2.34) from $94.2 million ($2.21) for 1984.

The per-share figures reflect a two-for-one stock split that Brunswick, which is based in Skokie, Ill., announced in December and that become effective Friday. Year-end sales were $1.54 billion, a 5 percent increase over $1.47 billion the year before. A lower effective tax rate was responsible for the company's increased net earnings, Brunswick President Jack Reichert said.

Brunswick reported strong sales and earnings gains by its defense division, a reduction in losses at the Brunswick division, which manufactures bowling equipment, and gains by the Technetics division, which produces filtration equipment and specialty materials. Mercury Marine also had another good year, Reichert said.

*Goodyear Tire and Rubber Co. reported 1985 earnings of $412.4 million ($3.84 a share) on sales of $9.6 billion compared with $411 million in earnings ($3.87) on sales of about $9.6 billion for 1984.

Per-share earnings dropped because additional shares were issued under Goodyear's dividend-reinvestment program, the company said.

For the fourth quarter, the company recorded sales of $2.48 billion, up from $2.42 billion for the final three months of 1984. Earnings were $84.5 million (78 cents), down from 1984's $105.3 million (99 cents).

Chairman Robert E. Mercer said the 1985 results were affected by significant costs that are expected to produce higher earnings in the future. Among those were after-tax costs of $45.8 million for various consolidation programs worldwide and the conversion of the Tyler, Tex., plant to radial-tire production.

*Western Union Corp. said it will post a $370 million loss for 1985 because of a fourth-quarter write-down of $300 million on certain switching and transmission equipment. Details of the results for all of 1985 will be announced in about two weeks, Robert S. Leventhal, chairman and chief executive officer, said earlier this week. Leventhal blamed some of the operating loss in 1985 on higher costs for leased telephone company facilities used to provide Western Union's telex and private-wire services, and reduced customer usage of those services.