With strong support from independents, Republican Linda McMahon leads Democrat Chris Murphy by three percentage points in the race for Connecticut’s open U.S. Senate seat in Quinnipiac University’s first poll of likely voters in 2012.

The poll released Tuesday found President Obama leading his GOP challenger, Mitt Romney, by a surprisingly close seven points, 52 percent to 45 percent. Obama carried the state by 23 percentage points in 2008.

“This smaller-than-expected margin for Obama could affect the Senate race,” said Douglas Schwartz, the poll’s director. “The Murphy campaign is hoping to benefit from Obama’s coattails, but right now they are not very long.”

The Senate results of 49 percent to 46 percent for McMahon are identical to last week’s Rasmussen poll, the latest sign she is now competitive in a blue state where she lost a Senate race by a crushing 12 percentage points just two years ago after spending $50 million.

“McMahon has worked on her image in the last two years, and it shows. Voters like her more now than they did when she faced Richard Blumenthal in 2010,” Schwartz said.

After struggling with negative favorability ratings for much of her first campaign, McMahon is viewed favorably, 47 percent to 35 percent. Murphy is viewed favorably, 38 percent to 30 percent, with 32 percent saying they do not know enough to form an opinion.

Those 32 percent of voters represent a potential upside for Murphy and a fat target for McMahon. She has been attacking Murphy in TV commercials since well before the Aug. 14 primaries, trying to define the 5th District congressman while he still is relatively unknown statewide.

With a 4-1 advantage in spending, the self-funding McMahon was on the air early, first with softer ads aimed at rehabilitating her image after the 2010 race, when her business success as a co-founder of World Wrestling Entertainment ultimately was judged a liability.

Murphy has yet to attack McMahon, other than running a commercial accusing her of misrepsenting his attendance record in Congress. McMahon already is on the air with a response ad, quoting a Hartford Courant analysis of her commercial as being “generally accurate.”

The seat is now held by the retiring Sen. Joseph I. Lieberman, one of two independents who are members of the Democratic caucus, giving Democrats their 53-47 majority.

The last time a Senate seat shifted from Democratic to Republican control in Connecticut was in 1970, when Lowell P. Weicker Jr. unseated a weakened Tom Dodd, who ran as an independent after being denied the Democratic nomination. Weicker lost to Lieberman in 1988.

The margin of error in the telephone survey of 1,427 likely voters is plus or minus 2.6 percentage points. It was conducted from August 22 to 26. With a different methodology that attempts to screen for likely voters, it cannot be directly compared to previous Quinnipiac polls this cycle.

The poll found Republicans unifying more quickly around their nominee after her primary victory over former Congressman Chris Shays.

She is supported by 88 percent of Republicans, compared to 82 percent of Democrats supporting Murphy, who defeated former Secretary of the State Susan Bysiewicz in the Democratic primary. McMahon has a 15-point lead among independents, 55 percent to 40 percent.

Her WWE affiliation remains a negative, though a slight one: 30 percent say it makes them less likely to vote for her, with 21 percent saying it makes them more likely to support her. Nearly half say the WWE is not a factor.

McMahon has turned a corner on other factors: half of Connecticut voters now see her as having the experience to be a U.S. senator, and 56 percent say they believe McMahon cares about the needs and problems of people like them.

By one measure, Murphy’s congressional experience is seen as a slight plus, with 33 percent saying it makes them more likely and 24 percent saying it makes them less likely to vote for him. But 51 percent of voters say they generally prefer a Washington outsider to someone with government experience.

The dynamic in the race is far different than in 2010, when her opponent was Blumenthal, a popular attorney general for 20 years and one of Connecticut’s best-known politicians. Her high-water mark in the Quinnipiac poll two years ago came in late September, when she closed to 3 percentage points.

In both the Senate and presidential races, there remains a significant gender gap, with women breaking Democratic and men going Republican, though McMahon is performing better among women than two years ago.

McMahon trails Murphy among women just 50 percent to 46 percent. Her lead among men is 54 percent to 42 percent.

Obama is overwhelmingly favored by women, 58 percent to 38 percent. Romney is more narrowly favored by men, 53 percent to 45 percent.

Echoing national polls, the Quinnipiac survey found the economy is by far the issue of greatest interest to voters, followed by Medicare — an issue very much in the news after Romney’s selection of Congressman Paul Ryan as his running mate.

A Pew Research Center poll last week found that 72 percent of Americans were aware of Ryan’s proposal to replace traditional Medicare with a voucher plan, which he has since revised.

Gov. Dannel P. Malloy, a Democrat who has been a campaign surrogate for Obama, on Monday called Ryan’s selection “the gift that keeps on giving.”

Neither running mate is providing a lift in Connecticut.

The new Quinnipiac survey found Vice President Joe Biden and Ryan with favorability ratings under water: 38 percent favorable and 43 percent unfavorable for Biden; 30 percent to 33 percent for Ryan, with 37 percent saying they do not now enough to form an opinion.

But by a margin of 43 percent to 35 percent Connecticut voters say that Biden is qualified to be president, while Ryan is viewed as qualified by 29 percent and unqualified by 26 percent. Forty-four percent are undecied on Ryan’s qualifications.

Obama is viewed favorably by 51 percent and unfavorably by 46 percent, while Romney has a negative rating of 41 percent to 44 percent.

The president is leading in every age, education and income group save one: He and Romney are tied among voters with annual household incomes greater than $100,000.

If he is to maintain the Democratic winning streak in Connecticut that began with Bill Clinton in 1992, the poll indicates the key will be getting out the state’s larger Democratic base. He trails Romney among independents, 49 percent to 47 percent.