American Telephone & Telegraph Co. reported yesterday that its second-quarter earnings rose 10.5 percent in what its chairman called "a difficult transition period." for the communications giant.

In other corporate earnings reports released yesterday, Citicorp, the nation's largest bank-holding company, said its second-quarter earnings soared 53 percent, while General Foods Corp. reported quarterly profits declined 3 percent.

The Bell System earned $1.93 billion in the second quarter on revenues of $17.5 billion, up from $1.75 billion in the year-ago quarter on revenues of $16.1 billion.

The 1983 quarter included a one-time $96.5 million charge-off for consolidation of some Western Electric operations. Per-share income in the quarter was $2.03 compared to $2.04 last year when there were 837 million shares compared to 933 million shares in the 1983 quarter.

"In earnings, as in other aspects of our operations, this is a time of transition for AT&T," said AT&T Chairman Charles L. Brown in referring to the company's divestiture of its Bell Operating Companies that will take effect on Jan. 1, 1984.

"Indeed, we have a couple of difficult years ahead of us," Brown said.

Although revenues for the system rose 8.3 percent in the quarter, operating expenses and taxes increased 8.5 percent to $14.7 billion from $13.5 billion in the same three months of 1982.

AT&T's average rate of return on capital of $122 billion was 9.72 percent, compared to a 9.94 percent return on capital of $115 billion last year. Return on its average $65.1 billion in common-stock equity was 11.63 percent compared to 11.93 percent last year on average equity of $57.3 billion.

The Bell System's six-month earnings were $3.67 billion ($3.91 a share), compared to $3.76 billion ($4.44) a year ago. Without a previously reported accounting change, Bell said earnings for the 1982 half-year would have been $4.10 a share. Revenues for the first six months rose 7.9 percent to $34.3 billion from $31.78 billion a year ago.

AT&T is the parent company for the 22 Bell operating companies, Western Electric and Bell Labs. Collectively, the parent and its subsidiaries are called the Bell System.

Citicorp's second-quarter earnings hit $210 million, despite a substantial tax increase and a widening increase in Latin American loan losses.

Citicorp, parent of Citibank, the country's second-largest bank, said first-half profit was $438 million, up 32 percent from $331 million. Second-quarter earnings per share were $1.59, up from $1.06.

Citicorp said the strong results for the first six months were achieved after providing $235 million for possible loan losses and absorbing an increase in income taxes of $182 million, bringing the effective tax rate to 48 percent from 40 percent.

Total provision for loan losses was $235 million in the first six months, a $65 million increase over last year, with net loan losses of $186 million and an addition of $49 million to the allowance, compared with net loan losses of $140 million and a $30 million addition last year.

Overall, the company's total provision for loan losses as of June was $729 million, up $128 million from the previous year. Assets were $130 billion, up $10 billion.

General Foods Corp., citing costs associated with marketing several new and expanded products, said its profit declined 3 percent in its first fiscal quarter despite a 4 percent revenue rise.

The company said its profit for its first fiscal quarter ending July 2, fell to $59.7 million ($1.15) this year from $61.5 million ($1.24) last year. First quarter revenue rose to $2.14 billion from $2.06 billion last year.