A conservative group is withdrawing its support for President Bush's nominee to the U.S. Supreme Court, Judge John Roberts.

Public Advocate, which bills itself as a pro-family group, says it opposes Judge Roberts because he helped gay rights activists win a landmark Supreme Court case in 1996.

In that case, the court overturned an amendment to Colorado's state constitution that would have barred laws from protecting homosexuals from discrimination.

Mr. Roberts reportedly helped a lawyer prepare for arguments in that case. 

Other conservative groups have expressed disappointment, but say they stand behind Mr. Roberts' nomination.

The development comes as Democrats call on the Bush administration to release scores of documents from Mr. Roberts' 1989 to 1993 tenure as top deputy solicitor-general in the first Bush administration. 

The White House has delayed releasing the documents, which reportedly cover advice Mr. Roberts gave on cases including school prayer, abortion and affirmative action.