Some wealthy gay couples will pay an average of $3.3 million more in federal estate taxes this year upon the death of a spouse than their married heterosexual counterparts, a new study finds.

If the estate tax penalty remains in effect, affected gay and lesbian couples will be subject to a total of $237 million in additional taxes in 2009 — and more than $3.5 billion in added taxes over the decade by 2011, according to a study by the University ot California, Los Angeles, School of Law’s Williams Institute.

Currently, taxpayers with estates valued at less than $3.5 million are exempted from federal estate taxes. The tax is scheduled to be repealed in 2010 but will resume in 2011 with a $1 million exemption.

Because gay relationships are not recognized by the federal government under the 1996 Defense of Marriage Act, taxpayers in same-sex relationships who transfer their assets to a surviving spouse are not exempt from the estate tax. Other tax protections that allow married heterosexual couples to transfer a business to their children — even those who are not legal descendants of the surviving spouse — are not offered to gays and lesbians.

"Even in 2010, when the estate tax is currently slated to be repealed, federal law allows different-sex married couples to shelter an additional $3 million in capital gains when a partner dies," said Michael D. Steinberger, the study’s author. "Regardless of your views about this tax, it is a costly implication of legal discrimination against gay and lesbian couples."

The report, funded by Merrill Lynch Global Wealth Management, is available here.