WASHINGTON — President Barack Obama on Sunday marked the 39th anniversary of the Supreme Court decision legalizing abortion by affirming his backing for the right, for decades one of America's most polarizing issues.

"As we mark the 39th anniversary of Roe v. Wade, we must remember that this Supreme Court decision not only protects a woman's health and reproductive freedom, but also affirms a broader principle: that government should not intrude on private family matters," Obama said in his statement.

"I remain committed to protecting a woman's right to choose and this fundamental constitutional right," the president said.

Abortion is invariably a bitterly debated issue every presidential election year, with conservatives eager to repeal the right and liberals insisting it is a fundamental right to be protected at all costs.

The president's statement that he is dedicated to American women's continued right to terminate an unwanted or medically risky pregnancy seemed destined to win the approval of his core Democratic supporters and socially liberal independents seen as key to his 2012 reelection prospects.

But his statement also acknowledged the "sensitive and often divisive" nature of the abortion debate in the United States.

"We must stay united in our determination to prevent unintended pregnancies, support pregnant woman and mothers, reduce the need for abortion, encourage healthy relationships, and promote adoption," the president said.

Pro-choice and anti-abortion protests and rallies were expected across the United States, including a huge planned rally at the US Supreme Court Monday.