SAN ONOFRE - The chairman of the Nuclear Regulatory Commission is scheduled to visit the troubled San Onofre Nuclear Generating Station today, joining NRC inspectors who have been investigating a small leak at the plant in northern San Diego County for the past two months.

Gregory Jaczko is scheduled to be accompanied by Democratic Sen. Dianne Feinstein and Republican Rep. Darrell Issa in his discussions with plant managers.

"They are going to be discussing the issues of the steam generators," in which hundreds of tubes have shown unexpected wear, agency spokesman Victor Dricks said. Testing of Unit 3 has found excessive wear in several relatively new steam generator tubes, of which each unit of the plant has thousands.

Station operators discovered the leak in one of the plant's units on Jan. 31, prompting an immediate shutdown of that unit.

The plant, which sits between San Clemente and Camp Pendleton, operates only two units -- Unit 2 and Unit 3. Unit Advertisement

[ Carrington Home Loans ] 1 was in operation from 1968 to 1992, when it was shut down over fears it could not withstand a major earthquake. Unit 2 was taken down for planned maintenance Jan. 9 and remains offline.

Late last month, the NRC ordered plant operator, Southern California Edison, to keep the power plant offline until the troubles with the plant are fully diagnosed and corrected. Edison officials responded by saying they would consider contingency plans in case the plant cannot be fully operational in time to meet summer demands.

Among possible contingency plans under consideration was the idea of buying power from another source and encouraging more conservation among customers, Edison spokeswoman Jennifer Manfre has said.

The environmentalist groups San Clemente Green and Friends of the Earth are demanding a full accounting of what went wrong at the plant. The FOE has been running a television ad that contends SCE is rushing the plant back into service, a charge the utility denies.