MADISON, Wis. (AP) -- The call for change in how Wisconsin Supreme Court justices are selected continues to grow as money pours into the race from shadowy interest groups.

The candidates themselves -- Justice Louis Butler and Burnett County Circuit Judge Michael Gableman -- spent less than $87,000 on television ads through March 16, according to one study.

But four independent groups that don't have to report to the state where their money is coming from or how much it is spending, funneled nearly $1.5 million into TV ads, said the report from the Brennan Center for Justice at New York University's School of Law.

That is roughly double what both candidates combined have raised throughout the entire race, reports filed Monday with the state showed.

The massive influx of spending from outside groups, along with the negative tone of many of their ads, has led to renewed calls for changes in how justices get on the bench in Wisconsin.

Good government groups including Common Cause Wisconsin and the Wisconsin Democracy Campaign are advocating for public financing of Supreme Court races. In December all seven members of the Supreme Court, including Butler, signed a letter also supporting some form of public financing for the high court.

A public financing bill even passed the Democratic-controlled state Senate this year but died in the Republican-led Assembly.

Others, including the state's second largest newspaper the Wisconsin State Journal, want to scrap the entire election process.

The newspaper, which declined to endorse either candidate, is calling for a merit selection system to pick judges.

That method, which usually involves a nominating committee that provides a list of finalists for the governor to appoint, is used by 24 states. Wisconsin is one of 13 with nonpartisan elections. Another eight have partisan elections and justices are appointed in five states.

State Rep. Fred Kessler, D-Milwaukee, said he will propose a constitutional amendment to give the governor the power to appoint Supreme Court justices in Wisconsin. The proposal by Kessler, a former Milwaukee circuit court judge, would have to pass both houses of the Legislature two sessions in a row and be approved by voters before taking effect.

This is the second year in a row that the battle for Wisconsin's highest court has been expensive, partisan and highly divisive.

Last year's race broke records both with how much the candidates spent and the total poured into the contest overall. Both candidates last year -- Annette Ziegler and Linda Clifford -- spent about $2.7 million while outside groups put in another $3.1 million.

This year's contest hasn't seen the same level of spending by the candidates.

Reports filed with the state on Monday show that Butler raised about $470,000 through March 17 compared with $278,000 for Gableman. Butler reported having $228,000 cash on hand compared to $121,000 for Gableman in the final days of the race.

The election is April 1. The winner will serve a 10-year term on the bench.

Mike McCabe, executive director of the government watchdog group Wisconsin Democracy Campaign, said he expects that outside groups will spend far more on this race than they did last year. But he said the candidates will spend less than their counterparts last year.

Three anti-Butler groups -- Wisconsin Manufacturers & Commerce, Wisconsin Club for Growth and the Coalition for America's Families -- spent about $974,000 on TV ads through March 16, according to the Brennan Center study that used data from TNS Media Intelligence. That compares with about $520,000 spent by the anti-Gableman group the Greater Wisconsin Committee.

"I am being drowned out and my opponent is spending less than I am," Butler said Monday. "Nobody is hearing from the candidates."

While the race is officially nonpartisan, Republican and business interests have lined up behind Gableman. He was first appointed to the bench in 2002 by then-Gov. Scott McCallum, a Republican.

Butler was appointed to the Supreme Court by Democratic Gov. Jim Doyle in 2004.

Doyle, who pledged on Monday to do whatever the campaign asks of him to get Butler elected, was scheduled to host a Butler fundraiser on Monday night along with U.S. Sen. Russ Feingold, D-Wis.

Butler's campaign says all levels of donations are accepted.

(Copyright 2008 by The Associated Press. All Rights Reserved.)