President Ford said yesterday he would veto any mandatory gasoline rationing bills voted by Congress, and rejected demands from Democratic Congressmen that he delay imposing tariffs on imported oil.

Ford also said, at his afternoon press conference, he would ask Congress for another $300 million in military aid to South Vietnam, but twice avoided answering questions on whether bombing raids would be resumed against the North Vietnamese.

Ford said he will sign an executive order this week to impose tariffs on crude oil imports--starting at $1 a barrel on February 1,going to $2 on March 1, and to $3 on April 1.

"There would be simply not enough gasoline to go around" with rationing, which "would limit each driver to less than nine gallons a week,"he said.

Ford also reiterated that the danger of war in the Middle East "is very serious" and said the administration is intensifying diplomatic efforts with Israel and some Arab states.

He also said he is disappointed with the Soviet Union's rejection of the 1972 trade agreement, which the Soviet government said impinged upon its internal affairs, but Ford said detente will be "continued, broadened and expanded."

Ford said he will seek deferral of action on national health insurance proposals because of projected budget deficits of $30 billion this year and $45 billion next year.

Sen. Henry M. Jackson (D-Wash.), a leading critic of Ford's energy program, said "no one up here that I know is advocating mandatory gas rationing." He said the President was trying to contend that rationing was the only alternative to import taxes."It's a straw man," Jackson said.