Profits of The Washington Post Co. last year doubled over 1975 to a record $24,5 million ($2.75 a share) compared with $12 million ($1.27), a gain the communications firm yesterday attributed to higher revenues and profits in all major divisions.

Times Mirror Co., of Los Angeles, also reported yesterday that 1976 produced record saled and profits. The publisher of The Los Angeles Times said profits totaled $69.5 million ($2.0 a share) compared with $47.8 million ($1.40) in 1975.

Included in the Post Co.'s 1976 results was a one-time gain of $1.8 million (20 cents a share) from the sale of radio station WCKY in Cincinnati. Without this nonrecurring increase, the Post Co. earned $22.7 million ($2.52 a share) in 1976, up 88 per cent fron 1975 and also up 57 per cent from the previous record year of 1974, when the firm, earned $14.4 million.

The Post Co. also reported yesterday that average circulation of The Post newspaper reached a record high of 560.249 daily and 765.243 on SUndays in the three months ended Dec. 31. The daily average was up 47,953, ot 9.4 per cent, from the 1975 period, when circulation was depressed by a strike of the pressmen's union.

Reveues of the company totaled $375.7 million last year, an increase of 21.5 per cent over $309.3 million in 1975, when operations of the firm were adversely affected by the national recession and strikes at The Washington Post Newspaper and Bowater Mersey Paper Co., Ltd., a Canadian newsprint affiliate.

For the fourth quarter of the year the Post Co. reported profits of $9.4 million ($1.05) compared with $5.5 million (59 cents) a year earlier, and increase of 70 per cent. Revenues rose 29 per cent to $111 million.

In addition to The Post newspaper, the Washington firm owns Newsweek magazine, the Trenton (N.J.) Times, and a group of broadcasting stations including WTOP AM-TV here.

According to yesterday's announncement, revenues and operating profits rose substantially at all three key divisions. Newspaper operating profits rose to $11.8 million form $6.6 million a year earlier; magazine and book operating profits rose to $21.4 million from $11.9 million rose to $15.8 million from $8.3 million.

Newspaper division advertising revenues rose by $22 million or 30 per cent over 1975, with total ad lineage up about 12.5 per cent at The Post and 21 per cent at the Ternton newspaper. The company's earnings statment attributed half of the lineage gain at The Post to recovery from strike conditions. Post retail and classified ad rates also were boosted by 9.5 per cent last Apri1.

According to Media Records. Post and lineag in 1976 totaled 82.5 million up 9.2 million lines from 1975 and equal to 66.2 per cent of the daily newspaper market. Washington Star ad lineage rose 5.9 per cent in 1976 to 45 million.

The communications firm said Post newspaper circulation revenues in 1976 increased last year but that expenses rose by the same amount, because of a change to a wholesale pricing structure.

Effective Feb. 1, The Post increased combined daily-Sunday and daily-only home delivery rates and began billing every four weeks instead of monthly. Daily and Sunday delivery is now $5.60 every four weeks (up from $5 monthly) and daily-only is $3.60 each four weeks (up from $3.35 monthly).

Post newspaper general manager Donald E. Graham said yesterday that the home delivery rate boost, the first since mid-1974, was based primarily on an increase in newsprint costs of about a third over the same period. Home delivery customers were "not infact compensating us for the newsprint delivered to the door," not counting all other expenses," Graham stated.

He said the new home delifery price of 15 cents daily is "a pretty terific buy" and "still cheaper than at the newsstand." Graham declined to comment on a company announcement that the higher home delivery rates" will make possible increases in earnings for cariers," citing current litigation involving some distributors.

A spokesman for the Washington Star said yesterday his newspapers had not prepared a supplementary report on circulation for the three months, ended Dec. 31, The latest Star data, filed with the Audit Bureau of Circulation, showed average Monday-Friday Circulation of 385.240 and Sunday Circulation of 374.267 for the six months ended Sept. 30.

The Post Co.'s broadcasting division reported a 24 per cent increase in revenues last year with TV revenues up 28 per cent. Newsweek ad revenues jumped 23 per cent with domestic editions carrying 2.887 pages of ads compared with 2.561 in 1675. The Newsweek book operations, which had been unprofitable in 1975, returned to the black last year.

Martin Cohen, vice president for finance said the 1976 return on equity for the Post Co. was about 20 per cent compared with 12 per cent in the strike-depressed 1975 and 16 per cent in 1974.

Time Mirroe Co. chairman Franklin D. Murphy said his firm's revenues rose 21 per cent in 1976 to $976 million. Most of the gains came in newspaper publishing and newsprint and forest products he said.

For the final quarter of the year, Times Miurror earned $20.5 million (60 cents) on sales of $261 million compared with year-earlier profits of $12.2 million (36 cents) and sales of $21 million.