A leading Democratic politician has said the President-elect of the United States was wrong to ask an evangelical preacher who likened gay couples to incest to participate in his inauguration.

Barney Frank, chairman of the US House of Representatives Financial Services panel, is one of two gay people in Congress.

In January he and Congresswoman Tammy Baldwin will be joined in the House of Representatives by a third, Jared Polis.

President-elect Barack Obama has chosen Rick Warren to lead the invocation at his January 20th inauguration in Washington DC.

“Mr. Warren compared same-sex couples to incest,” Congressman Frank said.

“I found that deeply offensive and unfair.

“If he was inviting Rev Warren to participate in a forum and to make a speech, that would be a good thing.

“But being singled out to give the prayer at the inauguration is a high honour. It has traditionally given as a mark of great respect.

“I think it was wrong to single him out for this mark of respect.”

President-elect Obama has defended his choice.

“We’re not going to agree on every single issue, but what we have to do is be able to create an atmosphere where we can disagree without being disagreeable, and then focus on those things that we hold in common,” he said.

He cited Mr Warren’s decision to invite him to speak at his chuch in California even though “I have views that were entirely contrary to his when it came to gay and lesbian rights, when it came to issues about abortion.”

The preacher echoed that sentiment in a statement.

“I commend President-elect Obama for his courage to willingly take enormous heat from his base by inviting someone like me, with whom he doesn’t agree on every issue,” he said.

Human Rights Campaign, America’s largest LGBT advocacy group was unhappy about the choice of Mr Warren.

“Your invitation to Reverend Rick Warren to deliver the invocation at your inauguration is a genuine blow to LGBT Americans,” HRC president Joe Solomonese said in a letter to Barack Obama.

“Our loss in California over the passage of Proposition 8 which stripped loving, committed same-sex couples of their given legal right to marry is the greatest loss our community has faced in 40 years.

“And by inviting Rick Warren to your inauguration, you have tarnished the view that gay, lesbian, bisexual and transgender Americans have a place at your table.

“Rick Warren has not sat on the sidelines in the fight for basic equality and fairness.

“In fact, Rev. Warren spoke out vocally in support of Prop 8 in California saying, “there is no need to change the universal, historical definition of marriage to appease 2 percent of our population … This is not a political issue — it is a moral issue that God has spoken clearly about.”

52% of voters backed Prop 8 on election day in November. It denies same-sex couples the right to marry.

Last week the California Attorney General said Prop 8 is unconstitutional and gay rights groups have already mounted legal challenges with the state Supreme Court.

President-elect Obama will take the oath of office on January 20th as part of a huge inuaguration ceremony and celebrations in Washington DC.