Feinstein, a Democrat, made the announcement during a hearing before the Senate Judiciary Committee in Washington on President Bush's nomination of Idaho District Judge Randy Smith.
Bush nominated Smith to replace Judge Stephen Trott, who moved to Idaho from California after his appointment to the court in 1988. Trott declared senior status in December 2004, meaning he will take a much lightened caseload. Since then, Idaho has not had an active judge on the court.
Feinstein and Sen. Barbara Boxer, D-Calif., said the seat should go to a California judge because tradition holds that judgeships remain in the same state. They have been protesting since last March after they learned the seat was promised to Idaho.
''To allow a judge's personal choice of where to live to change the allocation of future Court of Appeals sets a dangerous precedent.
''As this nomination ignores the judicial needs of the 9th Circuit and the state of California, I must oppose it, and I intend to place a hold upon this nomination,'' she said.
Sen. Larry Craig, R-Idaho, said the seat does belong to Idaho since Trott was based in Boise for the 17 years he was on the court.
''In fact, the seat has resided in Idaho longer than it has resided in California,'' Craig told the committee. ''I don't believe any tradition was violated when President Bush nominated an Idahoan to the seat.''
The ranking Democrat on the committee, Sen. Patrick Leahy, D-Vt., said Bush should nominate Smith for the seat vacated by 9th Circuit Judge Tom Nelson, an Idaho-based judge who declared senior status in 2003. Boise attorney William G. Myers was tapped by Bush three years ago to succeed Nelson, but his confirmation has been held up by a threat of filibuster.