Two large communications firms --The Washington Post Co. and Times Mirror Co. of Los Angeles -- yesterday reported record fourth-quarter and annual sale and profits.

Similar records also have been reported by the Tribune Co. of Chicago, Knight-Ridder Newspapers, and Dow Jones & Co., all engaged in newspaper publishing and related media businesses.

A decline in profits was reported by Media General Inc., which the Richmond based company blamed on reduced earnings at a newsprint recycling division.

Washington Post Co. fourth-quarter profits rose 38 percent to $13 million from $9.4 million in the same period of 1976, as sales increased by 14 percent to $127 million. Earnings per share were $1.57 vs $1.05, a 50 percent increase that reflects in part a reduction in the number of shares outstanding at the end of 1977.

For the fiscal year ended Jan. 1, the Washington communications company reported profits of $35.5 million, a gain of 45 percent over $24.5 million the previous year. Revenues were up 16 percent to $436 million and earnings per share were up 54 percent to $4.18 vs. $2.72 -- again reflecting fewer shares outstanding after the company bought back some of its stock.

In the final quarter last year, there were an average of 8.26 million common shares or their equivalent outstanding compared with 8.97 million a year earlier.

A company statement noted that a one-time insurance payment in the second quarter of 1977 boosted annual profits by some $500,000, or 6 cents a share.

The Post Co. owns The Washington Post newspaper, Newsweek magazine, the Trenton (N.J.) Times and broadcast stations. Although the company statement showed increased revenues and pretax profits for all three major divisions, the most significant gain was in newspaper publishing.

Pretax earnings of newspaper operations increased 127 percent to $26.9 million in 1976, which was affected adversely in the first quarter by a strike against The Post. Newspaper revenues were up 18 percent during last year.

According to the statement, advertising revenues increased by $24 million, or 18 percent, with advertising lines up 11 percent in The Post and 5.6 percent in the New Jersey daily. The company said yesterday that "increased productivity at The Washington Post contributed significantly to the increased profitability of the newspaper division."

In an address to local investors last Saturday, Post Co. President Mark J. Meagher said he expected to improve on 1977 results this year, "although certainly not at the growth rate we've had in the past two years." Inparticular, he said Post productivity gains could not be duplicated.

Magazine division pretax profits rose by 24 percent last year to $26.6 million, which the company attributed to higher advertising and circulation revenues.Newsweek and revenues were up 17 percent.

In the Post Co's broadcasting division, pretax earnings were up 12 percent to $17.6 million as revenues rose by 4 percent. Post Co. equity in profits of affiliates increased because of higher earnings of Bowater Mersey Paper Co. of Canada, a newsprint manufacturing affiliate.

Times Mirror Co., publisher of the Los Angeles Times, Newsday (Long Island) and the Dallas Times Herald, became the first publicly traded newspaper publisher to top $1 billion in annual revenues during 1977.

Annual profits were up 36 percent to $96.1 million ($2.77 a share) from $70.7 million ($2.03) in 1976. Revenues were $1.14 billion compared with $984 million the previous year. In the fourth quarter alone. Times Mirror earned $25.5 million (74 cents) on revenues of $3.13 million compared with 1976 fourth-quarter earnings of $2.69 million (60 cents) on revenues of $263 million.

Although Times Mirror also is a major forest products firm. Chairman Franklin D. Murphy yesterday attributed the sharp gains of last year to newspaper publishing. Newspaper revenues rose by 18 percent to [WORD ILLEGIBLE] million and pretax earnings were up 58 percent to $31 million.

Murphy said his firm's newspapers ran 307 million lines of ads in 1977. 9 percent more than in 1976: advertising revenues were up 18 percent to $397 million. Times Mirror also is engaged in book and magazine publishing information services, broadcasting and cable television.

Tribune Co., publisher of the Chicago Tribune and New York Daily News, reported 1977 profits of $36.1 million, an increase of 33 percent over $42 million in 1976. Revenues for the privately held company -- which recently agreed to buy WDCA-TV (Channel 20) in Washington -- rose 11 percent to $898 million.

In the fourth quarter, Tribune Co. profits were up 17 percent to $20 million from $17 million as revenues rose by 12 percent to $257 million.

President Stanton R. Cook attributed the 1977 gains to stronger economic conditions and gains in all divisions -- newspaper, broadcasting and forest products.

Knight Ridder Newspaper of Miami, No. 2 among newspaper chains in daily circulation, reported 1977 profits of $61 million ($3.76 a share), up 28 percent from $52 million ($3.21) in 1976. Revenues rose to $752 million from $678 million.

Chairman Alvah H. Chapman Jr. said ad revenues increased by more than 13 percent but average daily circulation was up less than 1 percent.

Dow Jones & Co., publisher of The Wall Street Journal and Barron's, reported 1977 profits of $39 million ($2.49 a share, up 29 percent from $30.3 million ($1.91) in 1976 as revenues rose by 15 percent to $317 million.

Media General reported 1977 profits of $13.6 million ($1.82 a share) compared with $15.1 million ($2.07) in 1976, although revenues rose to $217 million from $199 million. The firm, owner of the Richmond newspapers, said newspaper and broadcast revenues and profits set records in 1977 but could not offset declining earnings in newsprint recycling.