The state of Washington on Monday lost an appeal to the Supreme Court (search) to save its wide-open primary election system, an expected setback that forces state leaders to find a new way for political parties to choose candidates for office.

The high court had already ruled that so-called "blanket primaries," which had also been used in Alaska and California, are unconstitutional.

Washington, the last holdout for blanket primaries (search), argued its system was different and urged the court to intervene to keep it intact. Justices declined, without comment.

The state's nearly 70-year-old system allows voters to pick nominees from any political party, which the Supreme Court said in 2000 violates the political parties' right to choose their own nominees.

Washington state lawmakers have been reviewing other options, like copying Louisiana's system which sends the top two primary vote-getters into the general election, regardless of their party label, or requiring voters to choose among candidates of one party only.

James Pharris (search), an assistant state attorney general, had told justices in a filing that the state wanted to encourage voters to go to the polls by giving them a broader choice of candidates. "This case involves fundamental issues at the heart of the democratic process," he wrote.

An appeals court had already ruled against Washington, citing the Supreme Court decision that states cannot force political parties to allow outsiders to help select their nominees.

Political parties oppose blanket primaries because voters who aren't party members can switch sides.

"Unaffiliated and rival party voters are not free to cross party lines to support a particular candidate at the expense of the associational right of political party adherents to select their standard bearer," justices were told by Washington Republicans.

Democrats had told the Supreme Court that Washington's system was much like the California one that was stuck down by the court in 2000.

The case is Reed v. Democratic Party of Washington State, 03-801.