Mid Atlantic Medical Services Inc., the Rockville managed-care company, announced a 2-for-1 stock split yesterday, its second split in eight months, in a bid to attract more small investors.

MAMSI said it would give a 100 percent stock dividend to shareholders of record July 5. The dividend is scheduled to be paid Aug. 5. MAMSI now has about 22.6 million shares outstanding.

The company operates MD IPA and Optimum Choice Inc., both health maintenance organizations; and Alliance PPO Inc., a network of doctors.

George T. Jochum, chairman, chief executive and president, said the company decided to pay the stock dividend in response to the broker community, which "advised us that MAMSI stock PTC would be more attractive to the retail buyer if it were available at a lower price." He called the dividend "appropriate, given MAMSI's past performance and confidence in our future performance."

MAMSI stock closed at $55, up 87.5 cents, in trading on Nasdaq yesterday. The company's stock price has more than doubled since its 3-for-2 split in October 1993.