Department of Defense officials from the Ford administration called for senate rejection of SALT II yesterday and said the United States should increase military spending by $40 billion -- or about 20 percent -- over the next two years.

Former Secretary of Defense Donald Rumsfeld and former Deputy Secretary William P. Clements told a news conference that increases of 3 percent to 5 percent a year, now being debated by Congress, would be insufficient to carry out an across-the-board modernization of nuclear and conventional military forces.

Clements, now governor of Texas, recommended that the defense budget be increased by about $20 billion a year for the next two years, with lesser increases indefinitely thereafter.

The Carter administration has pledged a 3 percent annual growth in the nation's defense budget, but several senators have insisted that it must be stepped up by at least 5 percent before they will support ratification of the treaty between the United States and the Soviet Union.

Runsfeld and Clements were joined yesterday in a news conference denouncing the pact by former secretary of the Army Martin R. Hoffman, former secretary of the Navy J. William Middendorf and former secretary of the Air Force Thomas C. Reed. As the ranking members of the defense hierarchy, all had supported the 1974 Vladivostok agreement between then-President Ford and Leonid I. Brezhnev. That agreement formed the basis for the strategic arms limitation treaty finally signed by President Carter and Brezhnev last June.