WASHINGTON — Rep. Lois Capps, D-Santa Barbara, accelerated an election-year challenge to her Republican opponent Abel Maldonado, by releasing more than a decades’ worth of tax returns and pressing Maldonado to do the same.

A velvet-gloved slap, Capps’ move served two campaign purposes. The release of the tax returns positioned the lawmaker sometimes voted nicest member of Congress near the high ground, even as it pointedly reminded voters that Maldonado has been mired in disputes with the Internal Revenue Service.

“In light of the many serious questions raised by his tax problems, Mr. Maldonado has (many) reasons to post his tax returns on his web site,” Capps’ campaign spokesman Jeff Millman said.

Millman further cast the challenge as a way for voters in the 24th Congressional District to “judge for themselves the extent to which (Maldonado) has avoided paying taxes under the current code and whether he would personally benefit from his proposals to change it.”

Last week, the Capps campaign released the congresswoman’s 2011 return to McClatchy newspapers. On Monday, the campaign released all returns going back to 1998, Capps’ first year in Congress. With the broader release, the Capps’ campaign urged Maldonado to release all his returns going back to 1994, his first year in public office.

Maldonado’s campaign agreed to make public the candidate’s latest tax filing as early as the week of June 18.

“We will be providing the return in the very near future,” Maldonado’s campaign manager Brandon Gesicki said Friday, adding that “we need a little time to get it together.”

Capps’ 2011 return shows total income, including from her congressional salary, rent and pension from prior work as a school nurse, of $235,755. She reported charitable contributions of $15,064.

In a personal financial disclosure statement filed as part of his candidacy, Maldonado reported receiving rental income of between $100,000 and $1 million and farming partnership income of between $15,000 and $50,000. Candidates need not report their charitable contributions on the disclosure statements.

“Abel has been extremely transparent,” said Buck McLeary, deputy political director of the National Republican Congressional Committee, “and at the end of the day I have a hard time believing any of this will matter to voters.”

Spanning San Luis Obispo and Santa Barbara counties, and including a sliver of Ventura County, the newly redrawn 24th Congressional District is cited by Republican campaign operatives as potentially one of their top pick-up chances in the state.

In the June 5 primary, Maldonado finished second to Capps with 29.9 percent of the vote. His fellow Republican, Santa Barbara resident Chris Mitchum, who has so far declined to formally endorse him, took 21.6 percent. Maldonado outspent Mitchum $234,961 to $25,610 for the primary election cycle, Federal Election Commission records show.

So far, taxes have played a role, but not a dominant one, in the race.

In his campaign materials, Maldonado says he would simplify the tax code and “eliminate the loopholes that take money out of our treasury and twist priorities.”

His campaign website does not specify any loopholes for elimination.

Capps’ official House website specifies 11 priority issues about which she offers some detailed discussion, but taxes are not one of these general categories.

Mitchum’s campaign made a point of noting Maldonado’s tax disputes, as does the Capps campaign on a regular basis. On Monday, the Capps’ campaign cited prior news reports and court documents as pegging the Maldonado tax liability at $4.2 million.

“This dispute involves a lot of very complex accounting issues that other small businesses are attempting to navigate on a daily basis. … I want this resolved, and the second we get a bill that correctly defines our tax liability, it will be paid,” Maldonado said in a statement in May.

While Maldonado was serving as lieutenant governor in 2010, media reports noted that the IRS had placed a $111,146 tax lien on the family’s 6,000-acre Santa Barbara ranch. Maldonado’s brother Frank took responsibility and the bill was paid.

In U.S. Tax Court, Maldonado and the family farming operation called Agro-Jal Farming Enterprises are currently fighting the IRS over some $470,000 in disputed taxes. The IRS says the money is owed for errors in some complex deduction and depreciation matters. Maldonado disputes this.

“I hope this incident helps educate people on the need for a simpler tax code that allows employers to focus on job creation,” Maldonado said in April, adding that he would be severing his relationship with Agro-Jal.