American Telephone & Telegraph Co. said yesterday it earned $5.67 billion in 1979 -- more than any other corporation ever made in a single year.

AT&T which is the largest company in the world on the basis of assets, said its annual profits were up 7.6 percent from the $5.27 billion it earned in 1978. Its earnings per share rose from $7.74 to $8.04.

AT&T Chairman Charles L. Brown called the results "creditable considering the sharp upsurge in costs due to inflation." He said the company's economic activity peaked in March and then leveled off.

Revenues rose 10.7 percent during the year, from $41 billion to $45.4 billion, AT&T said.

At the same time, Ohio Bell Telephone Co., an AT&T subsidiary, sold a $175 million issue of 40-year bonds with a record 12.7 percent yield to investors.

No other AAA-rated Bell system issue had ever yielded more than 11.47 percent. The high cost to the company reflected the rapid rise in long-term interest rates this year.

AT&T reports annual earnings on a calendar-year basis, but doesn't release quarterly earnings on the same basis. It previously reported quarterly earnings for the period that ended Nov. 30.

The largest amount ever made in one year by any company other than AT&T was the $4.3 billion earned by Exxon last year on revenues of $84.4 billion.

Brown said the growth in demand for Bell services continued to be strong throughout the year, and that long-distance calling rose 10.8 percent while the overall volume of business rose 9.7 percent.

Greyhound Corp. more than doubled its earnings last year to $2.80 a share from $1.33 in 1978 partly because the 1978 earnings were reduced by writeoffs on discontinuance of some operations of the Armour Food division.

Profits for the final quarter rose to 86 cents a share from 55 cents.

Net income for the year was $123.03 million on revenues of $4.71 billion, up from $58.35 million in 1978 on revenues of $4.359 billion.

Net income for the final quarter was $37.72 million on sales of $1.206 billion against $24.19 million a year ago on sales of $1.163 billion.

Chairman Gerald Trautman said Greyhound Transportation results were up 83 percent on the year even though the bus passenger business was still in the red through the first half of the year. The financial group had a 39 percent improvement in earnings, food service 31 percent, Armour 26 percent and bus manufacturing earnings 68 percent.

Lockheed Corp. said net earnings dropped 12.9 percent last year to $56.5 million, including $20 million of extraordinary tax credits in the last quarter.

In 1978, the aircraft and missile manufacturer earned $64.9 million, including $9.9 million from discontinued operations.

Operating earnings in 1979 totaled $36.5 million ($2.16 a share), down 33.6 percent from $55 million ($3.51) in 1978, the company said yesterday.

Lockheed Chairman Roy Anderson, who several months ago had predicted lower 1979 reslts, said manpower and material shortages boosted costs for L-1011 TriStar jetliner and resulted in a loss of $188 million. In 1978, the company lost $119 million on its TriStar program.

Excluding the TriStar program, profits from 1979 operations before other income, interest and income tax increased 20 percent to $311 million from $259 million in 1978, Anderson said.

Lockheed reported sales of $4.06 billion last year, up 16.7 percent from $3.48 billion in 1978. Sales to the U.S. government represented 57 percent of the total, foreign sales 34 percent and domestic sales 9 percent, Anderson said. The breakdown was about the same in 1978, he added.

Fourth-quarter operating earnings totaled $13.7 million (85 cents), down 17.5 percent from $16.6 million ($1.07) in the fourth quarter of 1978.

Including the tax credits, earnings for the last three months of 1979 reached $33.7 million ($2.24) compared with $13.9 million (88 cents) in 1978. Fourth-quarter sales were essentially unchanged from $1.04 billion in 1978, the company said.

American Cyanamid Co. said that a strong performance by its agricultural chemical division enabled it to push 1979 earnings up 8.1 percent on a 14.6 percent rise in sales.

Net income was $168.5 million ($3.52 a share) on sales of $3.19 billion, up from $155.9 million ($3.26) in 1978 on sales of $2.78 billion.

Fourth-quarter earnings were $45.5 million (95 cents) on sales of $857 million compared with $43.9 million (92 cents) a year ago on sales of $740.5 million.

Chairman James G. Affleck said the chemical company's other divisions had sales gains for the year but encountered squeezes, with only the agricultural chemcials producing significant profit gains.