The US Supreme Court refused Tuesday to block a law allowing same-sex marriages in Washington DC, clearing the way for the legislation to go into effect Wednesday.

Chief Justice John Roberts, in a three-page opinion that sidestepped the legal issues involved, said the matter should be decided by local courts and decision makers in the US capital city.

Roberts rejected a petition by opponents of gay marriage for a stay that would have prevented the law from taking effect.

"Without addressing the merits of petitioners' underlying claim... I conclude that a stay is not warranted, Roberts wrote.

Roberts responded to the emergency petition but said the full court would be "unlikely" to hear the case as presented.

He said that "as a matter of judicial policy if not judicial power it has been the practice of the Court to defer to the decisions of the courts of the District of Columbia on matters of exclusively local concern."

The ruling clears the path for same-sex couples to begin applying for marriage licenses as early as Wednesday in the city, which will join the states of Iowa, Connecticut, Massachusetts, Vermont and New Hampshire in allow gay marriage.

Roberts also refused an emergency request for a referendum on the question.

But he said the petitioners may be able to pursue a ballot initiative under the city charter to repeal the act.

Roberts noted that the law was adopted by the city council and placed before Congress for a required 30-day period of review, and that the Congress "has chosen not to act."

A separate petition for a ballot initiative "is now awaiting consideration by the DC Court of Appeals, which will need to address many of the same legal questions that petitioners have raised here," Roberts said.

"Unlike their petition for a referendum, however, the request for an initiative will not become moot when the act becomes law. On the contrary, the DC Court of Appeals will have the chance to consider the relevant legal questions on their merits, and petitioners will have the right to challenge any adverse decision" at the Supreme Court "at the appropriate time."