SAN DIEGO GAS <SDO> SEES DECISION HURTING NET San Diego Gas and Electric Co said a California Public Utilities Commission decision to reconsider allowing only 20 mln dlrs of the 69 mln dlrs in San Onofre nuclear station costs it disallowed makes it likely that earnings in 1987 will be reduced at least 36 cts per share. The company said if the decision to disallow the other 20 mln dlrs is not changed, earnings would be penalized by another 19 cts.