The Baltimore Gas and Electric Co. has restarted the second of its two reactors at Calvert Cliffs nuclear power plant.

Unit 2, idled for refueling and equipment repairs since March 1989, began producing power again late Saturday night and is running at 30 percent power, BG&E; said yesterday. The reactor is expected to gradually increase to 100 percent power over the next two weeks.

The restart should mean lower bills for customers. BG&E; has been buying replacement power from other utilities and has passed on those charges to consumers through its fuel adjustment surcharge.

The restart comes almost a month after BG&E; got permission from the federal Nuclear Regulatory Commission to return the reactor to service. NRC officials concluded that BG&E; had upgraded its operation enough to run the unit safely, despite two problems in March.

The plant remains on the NRC's "watch" list of nuclear plants that bear close monitoring because of management and safety problems.

A 1988 NRC report concluded that BG&E; placed power production over safety in its operation of Calvert Cliffs, and the utility has been fined more than $650,000 because of safety violations. But federal officials have noted improved performance since then. A decision is expected next month on removing Calvert Cliffs from the problem-plant list.

Unit 1, shut down for inspection after Unit 2's cracks were found, returned to service last October.