W.R. Grace & Co. has reported a 73 percent increase in first-quarter profits but said earnings would have been down 5 percent except for a one-time gain of $65.1 million from the disposition of a subsidiary.

Meanwhile, Union Pacific Corp. posted 38 percent lower first-quarter earnings, Burroughs Corp. said its profits rose 22 percent on a 31 percent increase in sales, and Penn Central Corp. reported that its profits rose 57 percent.

Grace said first-quarter net income totaled $144.2 million ($2.99 a share) compared with $83.6 million ($1.74) for the same period of 1981. Revenues fell 2 percent from $1.489 billion to $1.463 billion.

Grace, which has interests in chemicals, natural resources, retail stores and restaurants, said that, without the nonrecurring gain, its first-quarter profit would have been $79.1 million ($1.64). The one-time gain of $65.1 million came from the disposition of Grace's Chemed Corp. subsidiary.

Grace said the recession in the United States and Europe had resulted in a 14 percent drop in income for its specialty chemical business and a 47 percent decline for its agricultural chemicals operations. Its retail businesses also had lower earnings.

The company said its natural resources business was up 31 percent, while its restaurant profits also were up some.

Union Pacific Corp. said its first-quarter earnings and sales were down from last year because the recession reduced railroad traffic and cut into refinery operations.

Net income was $48 million (50 cents) compared with 1981 first-quarter earnings of $77.6 million (81 cents). Sales fell 15 percent to $1.28 billion from $1.51 billion.

Union Pacific's subsidiaries, Union Pacific Railroad and Champlin Petroleum Co., posted lows for the first quarter compared with 1981.

Union Pacific Railroad's net income was $25.7 million on sales of $490.0 million compared with 1981 first-quarter earnings of $43.1 million on sales of $552.4 million. "The depressed economy caused erosion in nearly every major category except trailer and container traffic, which rose 26 percent," Chairman James H. Evans said.

Champlin Petroleum Co. earned $5.5 million on revenues of $737.5 million in the first quarter compared with earnings of $26 million on revenues of $918.7 million last year. "Champlin's operating income of $87.1 million in exploration and production was slightly ahead of last year in spite of some price softness and lower demand," Evans added.

Burroughs Corp. earned $27.1 million (65 cents) in the first quarter compared with $22.3 million (54 cents) in the same period last year.

The producer of computers and office machines said the recent quarter's sales of $990 million were up 31 percent from 1981 first-quarter sales of $756.5 million.

Penn Central Corp., a diversified energy and manufacturing concern, said its first-quarter profits increase reflected in part the inclusion of earnings by GK Technologies, which Penn Central acquired at the end of last year's first quarter.

Net income rose to $47.7 million ($1.22) from $30.3 million (67 cents) a year earlier as revenue rose 36 percent to $844.9 million from $621.8 million.

The 1981 per-share figure was adjusted to reflect a three-for-two stock split last January.

Chairman Richard Dicker attributed the company's improved performance mainly to the first-time inclusion of GK Technologies' results and to "the outstanding performance" of another subsidiary, Marathon Manufacturing Co., which makes offshore drilling rigs.

The company said its earnings included an after-tax gain of $6.4 million (20 cents) on the sale of GK Technologies' 27 percent interest in Phillips Cables Ltd., a Canadian wire and cable manufacturer.