President Reagan branded opposition to Robert H. Bork as "pure politics" yesterday, while Sen. Edward M. Kennedy (D-Mass.) called the Supreme Court nominee "a judicial hyperactivist" who would "reverse decades of progress toward greater justice."

The Senate Judiciary Committee opens confirmation hearings Tuesday on Bork, now a federal appeals court judge here.

In remarks at a Rose Garden ceremony marking the signing of a Hispanic Heritage Week proclamation, Reagan said Bork's critics have been engaging in "highly charged rhetoric" that is "irrational and totally unjustified."

"This administration remains fully dedicated to freedom and justice for all," the president said. "Don't let anyone tell you that those we nominate to high positions, especially to the Supreme Court, do not share in our commitment to the ideals of freedom and equality that all Americans hold dear."

Reagan said Bork "has a superior intellect, a high moral character and is a champion of individual freedom. Any suggestion to the contrary is pure politics -- if politics can be pure."

Kennedy, meanwhile, said Bork's writings, speeches and court decisions show he is an "extremist" who is "deeply antagonistic to the role of the law and the courts in fundamental areas such as ensuring racial justice, protecting the rights of women and guaranteeing the liberty of individuals against oppressive actions by the government."

Speaking to 450 faculty members and students at Georgetown University Law Center, Kennedy said, "Robert Bork is a judicial hyperactivist who would overrule dozens of precedents and reverse decades of progress toward greater justice in America."

Kennedy, a Judiciary Committee member, is a leader of the Senate's anti-Bork forces. He likened White House efforts to portray Bork as a "moderate" to the administration's assertions in the Iran-contra affair that it had sold arms "to what it called Iranian 'moderates.' "

At a news conference at the National Press Club, representatives of 22 national women's groups urged the Senate to reject Bork's nomination.

Speakers for 10 of the organizations said this was the first time their groups had opposed a Supreme Court nominee. Membership in the 22 groups exceeds 2.6 million.

Kate Michelman, executive director of the 250,000-member National Abortion Rights Action League, said Bork's record over the years shows he lives in an "imaginary world" that he could make reality if elevated to the top court.

Among the groups lining up to oppose Bork are the American Association of University Women, B'nai B'rith Women, National Organization for Women, Mexican American Women's National Association, National Conference of Women's Bar Associations, 9 to 5 National Association of Working Women and Black Women's Agenda.