Undated (AP) _ Gannett Co. said Thursday that second-quarter earnings jumped 16.2 percent over the year-earlier period, primarily because of strength in its newspaper operations.

It was the publishing company's 79th consecutive quarter of rising earnings.

Gannett said earnings for the quarter ended June 30 totaled $89.7 million or 56 cents a share, up from $77.2 million or 48 cents a share in the comparable quarter of 1986. Revenues totaled $789.7 million vs. $716.2 million, a 10.2 percent gain.

For the first half of 1987, Gannett said earnings totaled $142.3 million or 88 cents a share, up 16.6 percent from $122 million or 76 cents a share earned in the first half of 1986. Revenues totaled $1.49 billion vs. $1.33 billion, a 12 percent gain.

Company officials said newspaper advertising was up 4 percent, reflecting strength in classified ad sales, and that broadcast revenues increased slightly in the quarter.

In addition USA Today, Gannett's national newspaper, reported its first profit in May and was close to breaking even for the quarter, the company announced.

Based in Washington, Gannett operates 90 daily newspapers, 39 non-daily newspapers, the newspaper magazine USA Weekend, eight television and 16 radio stations as well as a major outdoor advertising company.

Among other publishers, Arthur D. Little Inc. said Thursday that second- quarter earnings totaled $1.8 million or 69 cents a share, a 12.5 percent gain over the $1.6 million or 63 cents a share earned in the 1986 second quarter. Revenues totaled $69.3 million vs. $63.8 million, an 8.6 percent gain.

For the first half, Little's earnings totaled $3.7 million or $1.44 a share, a 60.9 percent gain over the $2.3 million or 91 cents a share earned in the 1986 first half, when earnings were depressed because of a lawsuit settlement. First-half revenues totaled $136.5 million vs. $120.5 million, a 13.3 percent gain.

Based in Cambridge, Mass., Little is the subject of a $128 million unsolicited takeover offer from Plenum Publishing Corp.