International Business Machines Corp. said yesterday its third-quarter profits climbed 36.3 percent from a year earlier on a 21.6 percent gain in revenue.

IBM, the world's largest maker of computers, cited "significant increases" in orders from a year earlier and strong deliveries of its 3081 mainframe computer and its 3380 computer memory storage device.

In other major earnings reports:

* CBS Inc. said its earnings plunged 68 percent to $18.5 million in the third quarter, affected by the costs of retrenchments in its cable television and recording ventures.

* Eastman Kodak Co. cited sluggish economies worldwide and start-up costs of new products, and said its third-quarter profit fell 9 percent from a year earlier as sales were unchanged at $2.54 billion.

* J.P. Morgan & Co., parent company of the nation's fifth-largest commercial bank, said its third-quarter net income soared 43.8 percent from a year earlier.

* Gannett Co., which last month began publishing its USA Today newspaper five days a week, reported an 8 percent gain in third-quarter earnings to $42.86 million.

* Time Inc., noting the continued depressed state of the forest-products industry, said its third-quarter earnings from continuing operations slipped 9.3 percent to $35.2 million.

IBM said its third-quarter profits were $944 million ($1.58 a share) compared with $693 million ($1.18) a year earlier. Revenue rose to $8.17 billion from $6.72 billion.

Nine-month profits rose 21.8 percent to $2.71 billion ($4.56) from $2.23 billion ($3.80) as revenue climbed 16 percent to $23.3 billion from $20.1 billion.

CBS Inc. said that profits for the third quarter of $18.5 million (66 cents a share) compared with $58.7 million ($2.11) in the third quarter of 1981. Revenue declined 2 percent to $958.1 million from $973.6 million.

Nine-month profits fell to $76.8 million ($2.74) from $122.3 million ($4.38), although revenue rose to $3 billion from $2.94 billion.

Eastman Kodak Co., the world's largest maker of photographic products, said third-quarter profits fell to $303.9 million ($1.87 a share) from $334 million ($2.07) a year earlier. Kodak said its profit from operations also fell 9 percent in the quarter, to $518.7 million from $567.1 million.

Nine-month net income fell 15.5 percent to $733.5 million ($4.51) from $867.6 million ($5.38), and sales edged down to $7.22 billion from $7.26 billion.

J. P. Morgan & Co., the New York-based parent of Morgan Guaranty Trust Co., said third-quarter net income rose to $106.1 million ($2.57 a share) from $73.8 million ($1.77) in the third quarter of 1981.

Citing improved net interest earnings, Morgan said income before investment securities transactions was up 45.2 percent to $116 million ($2.81) from $79.9 million ($1.92).

Nine-month net income was $279.3 million ($6.77), up 18.1 percent from $236.5 million ($5.74) a year earlier.

Income before securities transactions was $312.3 million ($7.57), a gain of 21.2 percent over 1981's nine-month total of $257.7 million ($6.25).

Gannett Co. third-quarter profits were $42.86 million (81 cents a share) on revenues of $368.14 million compared with $41.06 million (76 cents) a year ago on revenues of $335.59 million. The revenue gain was 10 percent.

Nine-month revenues were also up 10 percent to $1.091 billion from $989.85 million and net income was up by 8 percent to $124.78 million ($2.35) from $117.86 million ($2.17).

Time Inc. said its third-quarter earnings from continuing operations slipped 9.3 percent to $35.2 million (55 cents a share) from $38.8 million (63 cents) last year.

Net income rose 79.6 percent to $35.2 million from $19.6 million, which reflected an after-tax loss of $19.2 million (31 cents), mostly from the cost of closing down The Washington Star.

Revenue for the quarter edged up 8.5 percent to $877 million from $808 million last year.

Nine-month income from continuing operations fell 16.4 percent to $109.9 million ($1.73) from $131.4 million ($2.16).

Net income climbed 14.8 percent from $95.7 million ($1.57) last year when Time absorbed a $35.7 million (59-cent) loss from The Star and the closing of Time-Life films in 1981's first quarter.

Nine-month revenues were $2.59 billion, up 8.8 percent from $2.38 billion a year earlier.