Republic Steel Corp. lost $28.5 million in the first quarter compared with a profit of $32.6 million ($2.01 a share) in the same three-month period a year before as sales declined by 20.8 percent to $880.4 million from $1.1 billion in the 1981 first quarter.

Republic, the nation's fifth-largest producer of steel and No. 87 on Fortune magazine's list of the largest industrial corporations ranked by 1981 sales, attributed the loss to the severe slump in demand coupled with increased steel imports.

Shipments declined 29 percent to 1.3 million tons from 1.8 million tons in the same period last year. It was the lowest shipment level since the fourth quarter of 1971, Republic said.

Raw-steel production of 1.6 million tons dropped 35.1 percent from 2.5 million tons produced in the year-ago period.

In other first-quarter reports, profits rose 101 percent at Citicorp, by 67 percent at Uniroyal Inc. and by 56 percent at the New York Times Co., but fell 34 percent at Merrill Lynch & Co.

Citicorp, the country's second-largest bank holding company, said first-quarter consolidated income before securities transactions was $199 million ($1.55 a share), up from $97 million (77 cents) a year ago.

Citicorp cited increased net interest income, larger volume of earning assets and a year-to-year improvement of the interest-rate spread between the cost of funds and the yield on investments.

Citing investors' wariness, Merrill Lynch & Co., the nation's largest brokerage house, reported that first-quarter profits slipped 34 percent, even though revenue advanced 16 percent.

Merrill Lynch said quarterly earnings were $30 million (76 cents a share), down from $45.2 million ($1.17) a year earlier. Revenue was $1.03 billion, up from $891.3 million.

Uniroyal Inc. reported that profits increased 67 percent in the first quarter to $19.2 million (68 cents a share) from $11.5 million (39 cents) a year ago.

Profit would have slumped to an estimated $1 million, however, if Uniroyal had it not sold its interest in two commodity chemical units, the No. 3 tire maker said.

Sales declined to $485 million from $541 million.

First-quarter earnings of the New York Times Co. were up 56 percent from a year ago on a 16 percent gain on revenue.

The Times, which owns The New York Times newspaper, said quarterly profit was $19 million ($1.51 a share) compared with $12.1 million (98 cents), while revenues were $225.5 million compared with $195.1 million.

Newspaper profits were up 38 percent from a year ago on a 16 percent revenue gain. Advertising rate increases helped push magazine profits up 27 percent in spite of a drop in revenues.