WASHINGTON — Nearly two-dozen conservative Christian leaders have signed a letter to the Senate Finance Committee questioning an investigation into six large ministries that preach a gospel of prosperity.

The letter argues that the 6-month-old inquiry sets a dangerous precedent. It also suggests that the ministries were targeted for sharing "the same branch of evangelicalism" and promoting "socially conservative public policy positions such as support for the traditional definition of marriage."

Although the ministries under scrutiny are conservative theologically, they are not at the forefront of the culture wars issues championed by the leaders who are now rallying to their side.

The most prominent figures who signed the letter are Moral Majority co-founder Paul Weyrich, American Family Association chairman Don Wildmon and former Ohio Secretary of State Ken Blackwell.

"The ministries have been asked to produce financial records and internal documents in what appears to be an exercise in disproving their alleged guilt," the letter states.

The group repeats an argument by some of the targeted ministries — that the investigation falls short of the high bar the Internal Revenue Service has for justifying a church investigation.

Sen. Charles Grassley of Iowa, the ranking Republican on the Senate Finance Committee, sent letters to the six ministries in November seeking answers about spending on private planes, oceanside mansions and board oversight. The committee's Democratic chairman, Sen. Max Baucus, joined Grassley in asking for answers.

The six ministries in question — led respectively by Kenneth Copeland, Creflo Dollar, Benny Hinn, Eddie Long, Joyce Meyer and Paula and Randy White — have denied wrongdoing. Some have pledged full cooperation, and others have either refused or provided limited information.

Jill Kozeny, a spokeswoman for Grassley, said the investigation is not concerned with church doctrine but with the adequacy of tax-exemption laws that have not been substantially changed since 1968.