<Page>

                                                                     EXHIBIT 12a

                     PUBLIC SERVICE ELECTRIC AND GAS COMPANY
               COMPUTATION OF RATIOS OF EARNINGS TO FIXED CHARGES



                                                     For the Year Ended December 31,
                                                 ---------------------------------------
                                                  2003    2002    2001    2000     1999
                                                 -----   -----   -----   ------   ------
                                                                   
Earnings as Defined in Regulation S-K (A):

Pre-Tax Income from Continuing Operations        $ 376   $ 320   $ 324   $  994   $1,163
Fixed Charges                                      390     408     461      447      442
                                                 -----   -----   -----   ------   ------
Earnings                                         $ 766   $ 728   $ 785   $1,441   $1,605
                                                 =====   =====   =====   ======   ======

Fixed Charges as Defined in Regulation S-K (B)

Interest Expense                                 $ 390   $ 406   $ 458   $  444   $  440
Interest Factor in Rentals                          --       2       3        3        2
                                                 -----   -----   -----   ------   ------
Total Fixed Charges                              $ 390   $ 408   $ 461   $  447   $  442
                                                 =====   =====   =====   ======   ======

Ratio of Earnings to Fixed Charges                1.96    1.78    1.70     3.22     3.63
                                                 =====   =====   =====   ======   ======


(A)  The term "earnings" shall be defined as pretax income from continuing
     operations. Add to pretax income the amount of fixed charges adjusted to
     exclude the amount of any interest capitalized during the period.

(B)  Fixed Charges represent (a) interest, whether expensed or capitalized, (b)
     amortization of debt discount, premium and expense and (c) an estimate of
     interest implicit in rentals.