CHICAGO -- Roman Catholics in the United States are putting $6 billion a year less in the collection plate than they should be, largely because many have rejected church authority on sex and other matters, priest-author Andrew Greeley said this week.

Roman Catholics across the board give only half as much in proportion to their income today as they did 25 years ago and only half as much proportionately as do U.S. Protestants, Greeley said in his latest book, "Catholic Contributions: Sociology and Policy."

Greeley, whose sexy novels about venality in the church have been hot sellers around the world, said a review of existing polls and studies showed that at least half of the decline in giving is due to a rejection of authority.

He told a news conference that American Catholics have not kept pace with inflation in adjusting their contributions upward. A Catholic family with an income of $60,000 annually gives an average of $660 to the church, compared with $2,500 for a Protestant family in the same income bracket, he said.

A quarter of a century ago, he said, Catholics and Protestants gave about the same percentage of their incomes.

Greeley argues in his book that "the most useful explanation we have, accounting for half the slump, is a selective alienation related to a decline in acceptance of the Church's authority and especially its authority on sexual matters" such as birth control. Studies by Greeley and others show that American Catholics overwhelmingly ignore the church's ban on artificial birth control.

Greeley, a recognized sociologist, said in the book that lay Catholics complain about the quality of the church, the role of women and the church's "disregard of how important sex is in healing and sustaining marriage."

Many Catholics "feel that every time the pope opens his mouth it is either to put down women or to suppress freedom or to forbid married sex," he said.

Retired Bishop William McManus, who headed the diocese in Fort Wayne-South Bend, Ind., and who was once superintendent of Catholic schools in Chicago, wrote a commentary published as part of the book in which he disagreed with some of Greeley's conclusions.

He told the news conference the church has not done a good job of explaining its financial needs.