President Bush has nominated conservative Judge John Roberts to replace late chief justice William Rehnquist.
"I'm confident that the Senate can complete hearings and confirm him as chief justice within a month," Mr Bush said in a hastily called public appearance in the White House Oval Office.
Mr Roberts's nomination, just two days after the death of Chief Justice William H. Rehnquist, raised fears among Democrats about a rightward shift as Mr Bush fills two openings on the nine-member court.
Democrats have been frustrated by Mr Roberts's popularity and said the Senate must take a closer look at his new nomination.
Mr Roberts had originally been nominated several weeks ago to replace another Supreme Court judge who is retiring.
The Supreme Court resumes work October 3rd.
