A US federal judge has ordered South Carolina not to issue cross-adorned ''I believe'' car number plates, ruling it violates the constitutional separation of church and state.

US District Court judge, Cameron Currie, ruled that the state legislature - which voted unanimously last year to approve the number plates that include a cross in front of a stained glass window - had clearly given favoured government treatment to a single faith, and ordered to halt its issue.

"Whether motivated by sincerely held Christian beliefs or an effort to purchase political capital with religious coin, the result is the same," Judge Currie wrote in a 57 page order. "The statute is clearly unconstitutional, and defence of its implementation has embroiled the state in unnecessary (and expensive) litigation."

"Americans United for Separation of Church and State" (AUSCS), a religious liberty group that brought the legal challenge to the bill before the court, hailed the decision. ''This is great news,'' said its executive director, the Reverend Barry Lynn. ''Some officials seem to want to use religion as a political football … That's an appalling misuse of governmental authority, and I am thrilled that the judge put a stop to it.''

Christian rights activists decried the decision, and the lieutenant-governor of South Carolina, Andre Bauer, who initiated the legislation, said the lawsuit discriminated against persons of faith.