WASHINGTON — The Supreme Court refused on Friday to allow the Trump administration to immediately enforce its new policy of denying asylum to migrants who illegally cross the Mexican border.

The Supreme Court’s two-sentence order revealed a new dynamic at the court, with Chief Justice John G. Roberts Jr. joining the four-member liberal wing in refusing to immediately reinstate the administration’s asylum policy.

The chief justice, appointed to the court by President George W. Bush in 2005, is now plainly at the court’s ideological center, a spot that had long belonged to Justice Anthony M. Kennedy, who retired in July and was replaced in October by Justice Brett M. Kavanaugh.

The court’s ruling thwarted, at least for now, President Trump’s proclamation last month that only migrants who arrived in the United States legally or applied at a port of entry would be eligible for asylum. And it is likely to only heighten tensions between Chief Justice Roberts and Mr. Trump, for whom limiting immigration is a central concern and who has been quick to criticize judges who rule against his immigration programs.