With the backing of senior Reagan administration officials, a group of conservatives has begun a broad attack on what it perceives as the federal judiciary's activism and liberalism.

At a press briefing and luncheon Wednesday in the Senate caucus room, the Free Congress Research and Education Foundation launched a book entitled "A Blueprint for Judicial Reform."

Among the proposals by its two dozen authors are empowering Congress to override Supreme Court decisions by two-thirds majorities; allowing the removal of federal judges either by congressional or popular vote, and stripping courts of jurisdiction over school prayer, abortion or busing cases--as pending legislation also proposes.

Paul M. Weyerich, president of the foundation and an activist in many New Right groups, said the specific proposals might not gain ready acceptance but expressed confidence that merely raising the possibility of such changes "will have a tempering effect on the behavior of the judiciary."

Weyerich said the book and project were "greeted with great receptivity" at meetings in the past week with Attorney General William French Smith and presidential counselor Edwin Meese III. In two recent speeches Smith has argued that the courts should take "the groundswell of conservatism evidenced by the 1980 election" as a cue to curb "judicial activism."

The briefing drew observers from the American Bar Association, Common Cause and the American Civil Liberties Union, along with many representatives of conservative organizations. David E. Landau, the ACLU legislative counsel, said he viewed it as part of "a radical assault on the federal courts and the independence of the judiciary."

But Jules B. Gerard, a professor of law at Washington University in St. Louis and a contributor to the volume, dismissed the objections of the organized bar.

"They will oppose any effort to restrict the power of judges," he said, "for the obvious reason that the more power judges have, the more power lawyers have to influence social policy without resort to democratic processes."