A majority of Harvard Law School professors yesterday signed a statement urging Congress to "establish at once" an independent prosecuting office to continue the work of former Watergate prosecutor Archibald Cox '34.

The statement, signed by Albert Sacks, dean of the Law School, and 45 professors of Law, also urges the House of Representatives to set up a committee to investigate President Nixon's "possible involvement in the concealment of crimes" and to seek evidence necessary for investigation.

Laurence Tribe, professor of Law, who circulated the statement, said a possible refusal by Nixon to comply with a Congressional request for presidential documents would form the strongest possible grounds for impeachment.

In a separate statement released late yesterday, three Law School professors said it is the legal and constitutional right of Congress to charge the judicial branch with power to appoint a prosecutor insulated from executive authority.

That statement was issued in response to an argument made Wednesday by Alexander Bickel, a professor of Law at Yale, who argues that the prosecutorial function belongs solely to the executive branch.

Bickel told newsmen, "Judicial power is not compatible with the exercise of the hiring, firing and for all I know, the supervising of prosecutors."

The Harvard Freshman Council also voted yesterday to send a telegram to House Majority Leader Thomas P. O'Neill (D-Mass.), urging the House to impeach Nixon. The council passed the motion to send the telegram by a wide margin.