The DuPont Co. yesterday reported net income of $121 million for the first quarter of his year, down $16 million from the same 1976 period.

The firm reported preliminary earnings of $2.45 a share of common stock in the first three months compared with $2.80 a share in the first quarter last year. Earnings totaled $1.87 a share in 1976's fourth quarter.

Sale for the first three months of 1977 totaled a record $2.271 billion, 8 per cent higher than the $2.098 billion in the comparable quarter of 1976 and 11 per cent above the $2.055 billion of the fourt quarter of 1976, the company said.

Chairman Irving S. Shapiro attributed the decline to "the absence of significant earnings" from its fiber output which was affected by an industrywide drop in selling prices. Shapiro, however, said the firm's fiber business had a "nominal" profit in the quarter after operating at a loss since the middle of last year.

RCA Corp. yesterday said its first quarter earnings jumped 41 per cent over 1976, and the company predicted a record year.

Profits in the first quarter were $48.5 million (63 cents a share), up from $34.3 million (44 cents) the year before. Sale rose by 9 per cent from $1.3 billion to $1.4 billion.

RCA president Edgar H. Griffiths said divisions including the National Broadcasting Co., Hertz Corp. and RCA Records all turned in record performances.

United Technologies Corp., a diversified industrial conglomerate, yesterday reported record first-quarter earnings and raised its quarterly common stock dividend from 30 to 45 cents a share.

Net income was $45.7 million, up 27 per cent from $36.1 million for the first quarter of last year. Per-share earnings advanced to $1.41, a 15 per cent gain over $1.23 a year ago. Sales were a record $1.4 billion, up 14 per cent from the $1.2 billion in the first quarter for 1976.

United Technologies' new dividend is payable June 10 to shareholders of record June 1.

Philip Morris, Inc., a diversified tobacco and beverage producer, yesterday reported a 25 per cent gain in first-quarter profits over the same period a year ago.

Philip Morris said profits totalled $71.4 million ($1.19 a share), up from $56.9 million (96 cents). Sales rose 21 per cent to $1.14 billion from $942.8 million.

The company said the first-quarter gains came mostly from cigarette and beer sales.

Tire maker B. F. Goodrich Co. yesterday reported record first-quarter net income of $18 million ($1.19 a share), up sharply from $9.6 million (63 cents) in 1976. Its previous high for the quarter was $13 million in 1973.

The Akron-based firm reported sales of $537.9 million compared with $520.6 million a year ago.

Chairman O. Pendleton Thomas said the company increased tire sales to auto makers and expects radial tires to grab a bigger share of its total sales.

Chemical New York Corp., parent of the nation's fifth largest commercial bank, yesterday said first-quarter net income after securities transactions rose 19 per cent to $24.4 million ($1.68 a share) from $20.4 million ($1.41) a year ago.

But Chemical said foreign exchange losses restrained its profits growth. The net before securities transactions was 24.3 million ($1.67), up from $20.4 million ($1.42).

Pfizer, Inc., yesterday reported that first-quarter earnings rose 7 per cent to $40.4 million (58 cents a share) from $37.9 million (54 cents) last year.

Sales for the first quarter totaled $482.6 million against $455.1 million in the first three months last year, a 6 per cent gain.

Gannett Co., Inc., a nationwide newspaper group, yesterday reported first quarter earnings of $10 million, up 1 per cent over a year ago.

The earnings were equal to 45 cents a share compared with 40 cents on 1976 first-quarter income of $8.8 million.

This year's first-quarter revenue totaled $104.3 million, up 10 per cent from $94.8 million last year.

Eli Lilly & Co., yesterday reported record first-quarter consolidated sales of $399.9 million, an increase of 10 per cent over $362.9 million in the same period last year.

The company reported estimated net income for the first quarter was 3.5 million (92 cents a share) compared with $61.4 million (89 cents) last year.