"This is a surge for Lamont," said Quinnipiac University Poll Director Douglas Schwartz. "It's rare to see such a big change in a race."
Businessman Ned Lamont had support from 51 percent and Lieberman from 47 percent of likely Democratic voters in the latest Quinnipiac University poll — a slight Lamont lead, given the survey's sampling error margin of plus or minus 4 percentage points.
"He leads, but it's not a statistically significant lead," said Schwartz, adding the race is too close to call. Lieberman "has just as good of a shot right now as Lamont. He shouldn't give up and analysts shouldn't close the door on a Lieberman victory."
Lieberman had led in a Quinnipiac poll last month, 55 percent to 40 percent.
The new poll suggests that Lieberman still could win a fourth term, even if he loses the Democratic primary Aug. 8.
Lieberman filed papers last week that will allow him to petition his way onto the November ballot. The poll found that among all registered Connecticut voters surveyed, including non-Democrats, Lieberman had the support of 51 percent, followed by Lamont with 27 percent and Republican Alan Schlesinger with 9 percent.
The telephone survey of 2,502 registered voters, 653 of them likely Democratic voters, was conducted July 13-18. The margin of error for the overall survey was plus or minus 2 percentage points.
Lamont, a multimillionaire and founder of a cable television company that has wired college campuses, has gained national attention in his challenge to Lieberman. Liberal blogs have built Lamont up while taking shots at Lieberman for his support of the Iraq war and other moves perceived to support congressional Republicans and Bush.
"We think the voters of Connecticut are continuing to realize that Ned represents the kind of change they want in Washington," said Lamont campaign spokeswoman Liz Dupont-Diehl. "It's clear that Joe Lieberman is just interested in hanging on to power."
Lieberman campaign spokeswoman Marion Steinfels said the poll simply shows that the race is "competitive."
"We've been treating it that way, and we continue to work hard to make sure Joe Lieberman wins on Aug. 8," she said. The campaign announced Thursday that former President Clinton would help campaign for Lieberman.
Schwartz said Lieberman needs to encourage his supporters to vote on Aug. 8. Turnout for primaries is typically low in Connecticut.
"Probably for Lieberman, the best thing he can do right now is get out his troops," Schwartz said. "This is going to be about turnout right now."
Lieberman was the Democratic Party's vice presidential nominee in 2000 and ran for the presidential nomination in 2004.