Gov. Edmund G. Brown's nomination of a woman, Rose Bird, as chief justice of the state Supreme Court faced a severe test today as a special three-member panel began extensive hearings on her appointment.

The Commission on Judical Appointments, which has the power to quash the nomination, consists of two state judges and California Attorney General Evelle Younger, who is a leading candidate for the Republican nomination to oppose Brown in next year's gubernatorial race.

If confirmed, Bird will become the first woman ever to sit on California Supreme Court. Her nomination has aroused considerable opposition in conservative groups who criticize her liberal political views, lack of judicial experience, and her role last year in setting up the state's controversial Agricultural Farm Labor Board.

The commission's two judicial members are expected to split their votes, so Younger, 58, apparently holds the swing vote. Republican conservatives, including Younger's two main rivals for the gubernatorial nomination, have urged him to help quash the Bird appointment.

Last week, younger's Sacremento office released a letter critical of Bird written by Bishop Roger Mahony, a Catholic prelate who served as chairman of the farm labor board set up by Bird. Mahony questioned Bird's "emotional stability" and her "vindictive approach in dealing with all persons under her authority."

Despite the release of the letter and the political pressure, Younger remained publicly uncommitted on the Bird vote.