Atlantic Richfield Co., the nation's seventh-largest oil company, said yesterday that higher crude oil prices and increased production from Alaska's North Slope helped increase second-quarter earnings 67 percent to $434.8 million.

The Los Angeles-based company also raised its quarterly dividend 5 cents to 47 1/2 cents a share, payable Sept. 15 to holders of record Aug. 15. c

The report follows earnings statements from other major oil companies last week noting that higher world petroleum prices continued to boost profit gains.

Atlantic Richfield reported a 51 percent increase in revenues to $5.6 billion in the second quarter, against $3.7 billion a year earlier.

It reported net earnings of $260.4 million in the second quarter of 1979. Earnings per share were $1.75 in the latest quarter compared with $1.06 a share in the 1979 period. Per-share earnings reflect a two-for-one stock split in May.

Chairman Robert O. Anderson said the company's production from Alaska's Prudhoe Bay increased to an average 278,000 barrels a day during the second quarter, up 28 percent from a year earlier.

For the six-month period, Arco reported net income of $860.9 million ($3.48), up 71 percent from profits of $502.6 million ($2.05) a year earlier. Revenues rose 54 percent to $11.1 billion from $7.2 billion in the first half of 1979.

Reduced demand for fabricated copper products cut earnings of Kennecott Corp. sharply in the second quarter from a year ago, despite a $5.2 million profit realized on the sale of the Carborundum division's graphite electrode business.

Net income was $21 million (63 cents a share) on sales of $577.2 million compared with $33.3 million ($1.00) a year ago on sales of $628 million.

First-half profit was $82.5 million ($2.49) on sales of $1.22 billion compared with $54.5 million ($1.64) a year earlier on sales of $1.20 billion.

Production of refined copper was up 8 percent in the second quarter from a year earlier at 107,200 tons, but physical sales were only slightly higher.