3M Co. yesterday reported higher earnings and sales for its first quarter, but the firm's chairman was cautious about the outlook for the rest of the year.

Meanwhile, several other American firms reported higher quarterly earnings, including Borden Inc. and Ralston Purina Co., while PACCAR Inc. reported its earnings declined by nearly 34 percent.

3M's first-quarter net income rose 6.8 percent to $181 million ($1.58 a share) from $169 million ($1.46) in the same period last year. Sales for the St. Paul, Minn., firm increased 8.5 percent to $2.07 billion from $1.9 billion.

Allen F. Jacobson, chairman and chief executive officer, said the firm benefited from a more-properly-valued U.S. dollar, cost control and a "slightly stronger tone of our U.S. business in the latter half of the quarter."

Borden Inc. announced first-quarter net earnings of $36.7 million, up 5.8 percent from $34.7 million in the first quarter of 1985. Earnings per share increased 10.6 percent to 73 cents from 66 cents, reflecting a reduction of almost 2 million shares outstanding since the year-ago period. Adjusted for a 3-for-2 stock split to be distributed June 3, per-share earnings increased to 49 cents from 44 cents.

Sales for the quarter were $1.14 billion, up 5.6 percent from $1.08 billion a year earlier.

Chairman and Chief Executive Officer Eugene J. Sullivan, speaking at Borden's annual meeting, said the New York company's first-quarter operating income increased 16.2 percent to $92 million from $79.2 million. Corporate expenses, however, were $6.4 million higher.

Ralston Purina Co. reported a 7.3 percent increase in its fiscal second-quarter earnings, despite a 10.2 percent drop in sales. The company said net earnings were $61.8 million (83 cents a share), up from $57.6 million (73 cents) in the corresponding period last year. Sales for the period declined to $1.31 billion from $1.46 billion.

Earnings for the six-month period surged 68 percent to $236.1 million from $140.4 million in the comparable period last year. Earnings per share climbed 79 percent for the six months to $3.06 from $1.71.

PACCAR Inc. of Bellvue, Wash., one of the nation's largest manufacturers of trucks and heavy transport equipment, reported first-quarter earnings of $13.8 million (77 cents a share), down nearly 34 percent from 1985's $20.8 million ($1.15).

Sales dropped 29 percent to $348.3 million from $492.6 million in the first quarter of last year, the company said.

BellSouth Corp. said yesterday that its earnings grew 27 percent in the first three months of 1986 from a year earlier. The Atlanta communications concern reported after-tax income of $420 million ($1.37 a share) for the first quarter, up from $330.9 million ($1.10) in the same 1985 period.

BellSouth, the largest of seven regional telephone companies created by the breakup of American Telephone & Telegraph Co. in 1984, said first-quarter revenue came to $2.8 billion, up from $2.5 billion in the first quarter of last year.