Carl Bellini has resigned as president of Erol's Inc. Video Club after only a year with the troubled video retailer, and company founder and chief executive officer Erol Onaran will take over the post.

Robert Morick, Erol's vice president for marketing and merchandising, said yesterday that Bellini cited personal reasons for his resignation and that there was no conflict between Bellini and Onaran. Bellini was unavailable for comment yesterday.

No effective date has been set for the resignation, Morick said, and Bellini will remain president "for a number of months."

Industry analyst Frank Moldstad, editor in chief of Video Store Magazine, could offer no explanation for Bellini's resignation. He said Bellini seemed to have been doing "all the right things" for Erol's, restructuring the company and pulling back from some markets and consolidating operations.

Before he came to Erol's, Bellini was executive vice president of store operations for Revco Inc., the 1,800-store drugstore chain that is operating under bankruptcy court protection. Prior to that, he was group vice president of retail stores at Sherwin Williams Inc., where he oversaw 1,500 paint stores and 425 Gray Drug Fair stores.

Erol's in March laid off 75 people, or 20 percent of its staff at the firm's Springfield headquarters, because of the softening market for videocassette rentals and increased competition in the Washington market.

The company still employs 300 people in its headquarters, and some 2,000 people, mostly part-time workers, at its 207 stores.

Sharpened competition from such video retailers as Blockbuster Video has forced Erol's to drop its membership fee and try more aggressive marketing tactics, such as its policy of accepting video returns at any store, regardless of where a tape was rented, for an extra charge.

Some 62 million Americans own videocassette recorders, and the business saw a robust growth during the 1980s as video stores proliferated. The business is showing signs of slowing, however. Fairfield Research, a Lincoln, Neb., company that follows the business, said video rental activity grew only 4 percent last year and that the increase was primarily due to a rush of activity at year-end.