American Telephone & Telegraph Co. said yesterday it earned $1.38 billion in 1984, its first year of operation after divesting its 22 Bell System telephone companies.

Separately, BellSouth Corp., one of the seven regional holding companies set up to operate the 22 divested Bell System companies, said its 1984 profit totaled $1.26 billion.

Among other companies reporting earnings data yesterday were fast-food giant McDonald's Corp.; UAL, the airline holding company; aircraft maker Boeing Co.; the W. R. Grace Co. and Celanese Corp. chemical concerns; food products conglomerate Nabisco Brands Inc. and brokerages Merrill Lynch & Co. and E. F. Hutton Group Inc.

* American Telephone & Telegraph Co.'s profit trailed both its own initial forecast and current estimates of some Wall Street analysts. AT&T Chairman Charles L. Brown said, "We expected to do better.

"We intend to do better in 1985 and better still in the years ahead," Brown said in a statement. In the meantime, he said, "AT&T remains a financially strong company with nearly $40 billion in assets and excellent prospects in rapidly growing markets."

Shortly before the breakup, AT&T had projected a profit of $2.1 billion, or $2.02 a share, for 1984. AT&T's actual 1984 profit equaled $1.25 a share and came on revenue of $33.2 billion.

For the fourth quarter alone, AT&T's profit was $379 million (34 cents a share) on revenue of $8.41 billion.

The fact that AT&T's actual 1984 profit trailed the company's initial projection was not a surprise. Brown had said last April, after announcing AT&T's first-quarter results, that the company did not expect to meet the initial earnings forecast.

Through the rest of the year, AT&T's earnings varied widely, exceeding and then falling short of Wall Street forecasts.

"This was their first year as an independent company; they had no track record to measure how they might perform," said Steven Chrust, who follows AT&T for the investment firm Sanford C. Bernstein & Co. "Given the radically changing regulatory environment, it would have been virtually impossible to create a smooth earnings pattern."

BellSouth Corp. said 1984 earnings totaled $4.28 a share on revenue of $9.52 billion.

In the fourth quarter, Atlanta-based BellSouth said it earned $362.8 million ($1.22) on revenue of $2.52 billion.

Because of AT&T's breakup at the start of last year, the 1984 results for AT&T and BellSouth are not comparable to any 1983 periods.

* UAL Inc., parent of United Airlines, said its fourth-quarter profit climbed 19 percent to $67 million ($1.76) from $56.1 million ($1.54) a year earlier. Revenue was flat at $1.67 billion, compared with $1.66 billion for 1983.

United Airlines' fourth-quarter operating earnings rose to $131.1 million from $103.5 million a year earlier.

For the full year, UAL, which also has interests in hotels, real estate and business services, said net income was $282.4 million ($7.46) up sharply from $142 million ($3.88) in 1983. Annual revenue rose to $6.97 billion from $6.02 billion.

UAL said its 1984 results included a $96 million net reduction in expenses stemming from a previously announced decline in the amount UAL needed to pay into United Airlines' pension plan.

United Airlines' 1984 earnings from operations jumped to $564.1 million from $160.1 million in 1983. UAL said the airline's gain reflected the strong U.S. economy, improvements in United's cost structure and higher fares, which bolstered United's average yield.

* Boeing Co. said its fourth-quarter net income jumped 26.5 percent to $124 million ($1.27), from $98 million ($1.01) a year earlier. Sales rose to $3.33 billion from $2.73 billion in 1983.

For all of 1984, the aircraft maker said earnings from operations rose to $390 million from $355 million ($3.67) in 1983. But last year, a $397 million gain related to a change in the tax laws lifted 1984 net income to $787 million ($8.09).

Boeing's annual sales slipped to $10.4 billion from $11.1 billion.

Boeing said its 1984 improvement reflected a stronger airline industry, which benefited from growth in airline traffic, lower fuel prices and labor costs, and "a more stable fare structure."

* McDonald's Corp.'s systemwide sales for the year ended Dec. 31 increased 15 percent to more than $10 billion, compared with sales of $8.6 billion in 1983, the company said. Fourth-quarter sales jumped 13 percent to $2.5 billion, compared with $2.2 billion in the 1983 fourth quarter.

Net income during 1984 increased 14 percent to $389 million ($4.39), compared with $342.6 million ($3.83) in 1983. Fourth-quarter net income increased 14 percent to $91.2 million ($1.03), compared with $79.9 million (90 cents) in the 1983 fourth quarter.

Total revenue in 1984 increased 11 percent to $3.4 billion, compared with $3 billion in 1983. Fourth-quarter total revenue increase 10 percent to $859.7 million, compared with $783.1 million in the 1983 fourth quarter.

* W. R. Grace & Co., the diversified chemical company, reported that its fourth-quarter earnings rose 2 percent in 1984. Profits for the full year profits increased 22 percent over comparable 1983 levels.

In the final 1984 quarter, Grace earned $59.08 million ($1.22), up from $57.98 million ($1.19) in the final 1983 quarter. Sales advanced to $1.83 billion from $1.75 billion.

* Celanese Corp. reported a 38 percent decline in its fourth-quarter earnings.

Celanese reported its profit slipped to $32 million ($2.31) in the fourth quarter from $52 million ($3.25) a year earlier. Fourth-quarter sales fell 3 percent to $825 million from $850 million.

For the year, Celanese had profits of $161 million ($10.87), up 44 percent from $112 million ($6.89) in 1983. Sales rose to $3.33 billion from $3.26 billion.

* Nabisco Brands Inc. said net income for the fourth quarter ended Dec. 31 was $107.2 million ($1.79), an increase of 6.2 percent from $100.9 million ($1.56) for the year-ago period. Fourth-quarter sales were $1.72 billion, up 3.1 percent from $1.66 billion in 1983.

For the year, the company reported profits of $308.9 million ($5.02), a decrease of 4.2 percent from $322.6 million ($4.86) in 1983. Net sales for the year were $6.3 billion, up 4.5 percent from $6 billion in 1983.

* Merrill Lynch & Co. Inc., the nation's largest brokerage, said its 1984 net income plummeted 59 percent, although it managed to post a profit in the fourth quarter compared with a loss a year earlier.

Merrill Lynch said net income for 1984 totaled $95.3 million ($1.03), compared with $230.2 million ($2.68) in 1983. Revenue rose 6.2 percent to $6 billion from $5.7 billion in 1983.

Fourth-quarter net income came to $29.6 million (31 cents), compared with a loss of $42.1 million in the same period a year ago. Revenue for the three months rose 18 percent to $1.6 billion from $1.4 billion in 1983.

* E. F. Hutton Group Inc., the fifth-largest investment firm, said its net income for the year sank 52 percent despite an 187 percent spurt in fourth-quarter earnings.

Hutton said net income for the year fell to $52.7 million ($2.05) from $110.6 million ($4.42) in 1983. Revenue rose 27 percent to $2.8 billion from $2.2 billion.

Hutton said its fourth-quarter net income came to $24.3 million (94 cents), compared with $8.5 million (33 cents) for the 1983 period. Discounting the reserve in 1983, Hutton said its profits increased a more modest 38 percent from $17.6 million. Revenue soared 57 percent to $895 million from $571 million in 1983 last year.

The fourth-quarter jump in profits came largely from a reserve the company provided in 1983 for Baldwin-United Corp. annuity policies.

Baldwin-United filed for reorganization under Chapter 11 of the federal bankruptcy laws in September 1983. Last fall, several brokergage firms, including Merrill Lynch and Hutton, that had sold Baldwin-United annuities agreed to pay $135 million to settle suits stemming from the sales.