WASHINGTON (CNN) -- Nearly 70 percent of Americans oppose a presidential pardon for former White House aide Lewis "Scooter" Libby after his conviction on perjury and other charges related to a CIA agent's exposure, according to a CNN poll out Monday.

Just 18 percent said they would support a pardon for Libby, the former chief of staff to Vice President Dick Cheney, while 69 percent said they opposed the idea. Meanwhile, a narrow majority said they believe Cheney was part of a cover-up in the case.

The new poll was conducted for CNN by Opinion Research Corp. between Friday and Sunday. Pollsters quizzed 1,027 adults for the survey, which had a sampling error of 3 percentage points.

President Bush's job approval rating increased slightly, rising to 37 percent from the 34 percent he received in the earlier poll. Cheney's approval rating in the survey fell from 39 percent in a January poll to 34 percent in the latest survey, while 54 percent said they disapproved of the vice president's job performance.

Though he has a lengthy resume in Republican administrations dating back to Gerald Ford's presidency, 60 percent of those polled said they did not consider him qualified to serve as president should it become necessary; only 32 percent said he would be qualified to lead the country himself.

And asked whether the vice president was "part of a cover-up" to keep special prosecutor Patrick Fitzgerald from learning who leaked the identity of CIA agent Valerie Plame Wilson, whose husband had become a critic of the war in Iraq, 52 percent said yes; 29 percent said no. Another 20 percent had no opinion.

FULL POLL RESULTS (PDF)