Dart Group said its earnings soared in the second quarter, thanks to profits from the sale of its 5% stake in Supermarkets General in May. Dart earned $17.4 million during the quarter, compared to $99,000 a year earlier. Revenue rose to $98.7 million, up about $10.5 million from 1986. Landover, Md.-based Dart, which has boosted its earnings over the years by letting its takeover targets get away in exchange for healthy premiums, said six-month earnings also got a boost from the sale of its stake in Oakland-based Safeway Stores, the nation's largest supermarket chain. Earnings for the six months rose to almost $46 million from last year's $576,000.