By Susan Heavey
WASHINGTON (Reuters) - President Barack Obama has staked out a clear lead in Ohio, Pennsylvania and Florida - three battleground states in the November 6 U.S. election - over his Republican challenger Mitt Romney, a poll released on Wednesday showed.
The Quinnipiac University survey, taken just days after Obama's immigration policy announcement on June 15, also found strong support in all three states for the order allowing some illegal immigrants brought to the country as children to avoid deportation.
Overall, the poll found Obama ahead of Romney by 9 percentage points in Ohio (47 percent to 38 percent), 6 percentage points in Pennsylvania (45 percent to 39 percent) and 4 percentage points in Florida (45 percent to 41 percent).
The poll showed Obama holding a big lead among women, younger voters and blacks in the three states.
The results are outside the poll's margin of error of plus or minus 2.8 percent. Last month, Ohio and Florida had been too close to call, and Obama had led Pennsylvania by an even larger margin of 8 percentage points, according to the poll of nearly 3,700 voters.
The three states may be critical to winning the presidential election, and "no one has won the White House since 1960 without taking at least two of them," Quinnipiac said.
Obama is seeking a second four-year term in office and won all three in 2008. Nationwide polls have shown Obama and Romney in a tight race.
"If he can keep those leads in all three of these key swing states through Election Day he would be virtually assured of re-election," said Peter Brown, assistant director of the Quinnipiac University Polling Institute.
IMMIGRATION AND THE ECONOMY
The Quinnipiac poll surveyed voters from June 19 to 25, days after Obama announced that hundreds of thousands of illegal immigrants who were brought into the United States as children could be able to avoid deportation and get work permits. Most illegal immigrants in the United States are Hispanics.
Obama's action came amid Republican opposition in Congress to "Dream Act" immigration legislation supported by the president. Romney accused Obama of political motivation in making the policy change, but declined to say he would repeal it if elected.
"Voters in all three states voice strong support for the president's mini 'Dream Act' immigration order, and they say the president would be better than Romney handling immigration," Brown said.
In Florida, Hispanic voters said they would back Obama over Romney 56 percent to 32 percent - up 7 percentage points from another Quinnipiac poll earlier in June before the policy change.
More than half of the voters polled in Ohio and Pennsylvania also said they supported Obama's immigration policy.
The picture is less clear when it comes to the economy, a central theme ahead of the election as the nation struggles to recover from the worst recession in more than 80 years.
Voters in all three states were mixed on whether Obama or Romney would do a better job on the economy or improve their personal economic future.
Ohio voters gave an edge to Obama on the overall economy but backed Romney when it came to the impact on their personal situation. Florida voters said the opposite. In Pennsylvania, voters were equally split.
"For much of the last year, more voters in these swing states have said Romney would do a better job on the economy. That advantage has largely disappeared, at least for now," Quinnipiac's Brown said.
(Editing by Will Dunham)