U.S. Sen. Joe Lieberman, fighting for his political survival, appears to be cutting into challenger Ned Lamont's lead the day before Connecticut's Democratic primary election, according to a Quinnipiac University poll released Monday.

The poll shows Lamont, a wealthy Greenwich businessman, with a slight lead of 51 percent to 45 percent over Lieberman among likely Democratic voters heading into Tuesday's primary.

Last week's Quinnipiac poll showed Lamont leading 54 percent to 41 percent. Lamont also had a slight lead in Quinnipiac's July 20 poll.

"Obviously we are very thrilled," Lieberman spokeswoman Marion Steinfels said. "People who are making this decision are taking a serious look at Lieberman and Lamont and believe that Joe's the one who has been fighting for them."

A message was left with the Lamont campaign seeking comment.

Only 4 percent of respondents said they were undecided and 90 percent of voters who name a candidate say their mind is made up. In last week's poll, 5 percent of likely Democratic primary voters were undecided, but 85 percent of voters said their mind was made up.

Monday's poll also showed that the gubernatorial primary has also tightened up with likely voters backing New Haven Mayor John DeStefano 48 percent to 41 percent over Stamford Mayor Dan Malloy. DeStefano had a 48 percent to 38 percent lead in last week's poll.

In Monday's poll, 10 percent of respondents were undecided and 28 percent who already chose a candidate said they still might change their mind.

Lieberman, 64, one of the Senate's most well-known Democrats and his party's nominee for vice president in 2000, has been harshly criticized in Connecticut for his support of the Iraq war and his perceived closeness with President Bush and Republicans.

Lamont, 52, who owns a successful cable television firm, has been able to tap into rank-and-file Democratic voters' frustration with Lieberman as well as his personal wealth, contributing $3 million to his campaign.

Hedging his bets against a primary loss, Lieberman is also collecting signatures to petition his way onto the ballot as an independent should he lose Tuesday's primary. Unaffiliated voters outnumber Democrats and Republicans in the state and Lieberman has typically drawn strong support from both unaffiliated and Republican voters.

The telephone poll, conducted from July 31 to Aug. 6 of 784 likely Democratic primary voters, has a sampling error margin of plus or minus 3.5 percentage points.