Should the Senate fail to confirm John Tower, three names are frequently mentioned in Washington speculation about who President Bush would choose next as defense secretary.

Two are familiar - old Washington hands respected by both Republicans and Democrats who would have no trouble being confirmed - and the third is a corporate executive who is a strong advocate of Pentagon reforms.The White House is not believed to be seeking alternatives or even making initial contacts yet, since the president has pledged his full support for Tower.

But if the Senate fails to confirm Tower, Bush will have to find someone else to lead the Pentagon.

Most frequently mentioned are Donald Rumsfeld and James Schlesinger, both former defense secretaries, and Norman Augustine, chairman and chief executive officer of the Martin Marietta Corp.

Augustine, 53, was interviewed by Bush in early December for a top Pentagon job believed to be that of deputy defense secretary. No details were made public, but it was reported that Augustine balked at working for Tower and wanted the top post of defense secretary or nothing.

Augustine was undersecretary of the Army in President Ford's administration and was assistant secretary of the Army in the Nixon administration.

He left the government in 1977 to join Martin Marietta of Bethesda, Md., one of the nation's top aerospace and electronic companies and a major defense contractor, as vice president for operations.

Augustine became the company's chief executive in 1987 and is an outspoken advocate of defense reforms.

Rumsfeld, 56, is a former Republican congressman from Illinois. He headed President Nixon's economic stabilization program and is former U.S. ambassador to NATO and a former White House chief of staff. Now a senior adviser to the Chicago investment banking firm William L. Blair & Co., Rumsfeld established a reputation as a top administrator as President Ford's defense secretary.

Schlesinger, 60, has served in Democratic and Republican administrations. He has been defense secretary, director of the CIA and the nation's energy czar. He is currently a counselor in residence for the Center for Strategic and International Studies, a conservative think tank in Washington.