Chase Manhattan Corp., parent company of the nation's third-largest bank, said yesterday that its third-quarter operating earnings were up 19 percent from a year earlier, primarily due to higher interest income and other increased operating income.

And Bankers Trust New York Corp., holding company for the eighth-largest bank, reported a 41 percent gain in its third-quarter operating net.

Chase's consolidated income before securities transactions was $96.5 million compared with $81.2 million a year ago. Per-share net before securities transactions was $2.73, up 15 percent from $2.37 for the same 1979 quarter.

Provision for possible loan losses in the third quarter was $50 million, 39 percent higher than the $63 million provision a year ago. Net chargeoffs were $3.12 million versus $19.3 million in the third quarter last year.

Chase reported a gain of about $3.6 million in the third quarter on the repurchase of $30 million principal amount of 4.6 percent capital notes of Chase Manhattan Bank N.A.

Nine-month operating earnings were up almost 23 percent to $287.5 million ($8.36 a share) from $234.6 million ($6.83) in the comparable 1979 period.

Chase said net interest income on a taxable-equivalent basis for the third quarter was $463 million compared with $399 million a year ago. For the nine months, interest income totaled $1,325 billion versus $1,185 billion a year earlier.

Banker's Trust earned $3.33 a share in the third quarter plus 48 cents on the sale of branches compared with $2.36 a year ago.

For nine months, the bank holding firm earned $11.45 a share plus a $1.46 gain on the sale of branches, against $6.90 a share in the 1979 period.

The net operating income for the nine months was $139.9 million, up $55.7 million from a year earlier.

Chairman Alfred Brittain III said the rise in third-quarter operating net was caused by better net interest income and higher commissions and fees. These were offset to some extent by a loss on securities trading, lower net revaluation gains on foreign investments and a higher loan loss provision. Fully taxable net interest income was up 37 percent at $210.9 million in the quarter.

Strong sales gains in the second and third quarters improved the 1980 financial picture for Eastman Kodak Co., the world's largest manufacturer of film and cameras.

The company reported a 26 percent gain in net earnings to $358.8 million ($2.22 a share) from $285.9 million ($1.78) in the comparable year-ago period. Sales rose 18 percent from $2 billion to $2.36 billion.

Nine-month net income increased 20 percent from $706.1 million ($5.25) to $847.2 million ($4.38) and sales were up 22 percent to $6.63 billion from $5.44 billion.

Continental Group, the conglomerate built around Continental Can Co., earned $2 a share in the third quarter, up from $1.56 a year earlier on a rise in sales to $1.225 billion from $1.173 billion.

Nine-month profits were $148 million ($4.53 a share) on sales of $3.506 billion compared with $133 million ($4.09) on sales of $3.32 billion.

President S. Bruce Smart Jr. said most of the third-quarter profit gain resulted from the adoption of the Financial Accounting Standards Board's Rule 8 on foreign currency translations which raised 1980 third-quarter net 15 cents a share and lowered last year's third-quarter profit 23 cents a share. 1Continental has been a sharp critic of the rule.

Boise Cascade Corp., one of the nation's largest paper and lumber products firm, says its earnings for the third quarter declined 41 percent from the same quarter last year.

The company said Tuesday its net income of $29.5 million ($1.10 a share) compared with $50.4 million ($1.88) a year ago. Sales slipped from $776.7 milliion to $764.1 million.

Chairman John B. Fery attributed the decline in sales and earnings to a strike in Boise Cascade's paper business and the continued depression in the home-building industry, which hurt the building materials side of the company's business.

Nine-month earnings fell to $105.2 million ($3.94) from $138.8 million ($5.16) as sales rose from $2.16 billion to $2.21 billion.