Oklahoma voters gave overwhelming approval last night to a constitutional amendment that would limit state legislators to no more than 12 years in office.

The measure, the first in the nation to curb incumbents' hold on their jobs, won by 2 to 1.

In Washington state, former governor John D. Spellman (R) was hoping to find new political life on the state Supreme Court.

In Oklahoma, both parties also held runoffs to complete the process, begun in an Aug. 28 primary, of nominating a candidate to succeed Gov. Henry Bellmon (R), who is stepping aside.

On the Republican side, businessman Vince Orza had 49 percent and former U.S. attorney Bill Price had 51 percent with 92 percent of the vote counted. Both men are political newcomers from Oklahoma City.

The Democrats, meanwhile, gave 1986 nominee David Walters of Oklahoma City 51 percent to 49 percent and U.S. Rep. Wes Watkins of Ada.

The constitutional amendment bars future Oklahoma House and Senate members from serving more than 12 years. Current members may serve 12 more years after the measure takes effect Jan. 1. Similar measures are on the November ballots in Colorado and California.

The Oklahoma primary campaign was the most expensive in state history on both sides.

Both Watkins and Walters listed more than $1 million in contributions. The latest reports showed Price nearing $1 million in expenditures, while Orza reported about $315,000.

In Washington state, Spellman took a new political path when he challenged Supreme Court Justice Richard Guy. Guy was appointed to fill an unexpired term last fall by Gov. Booth Gardner (D), who ousted Spellman in 1984.