Former Defense Secretary Robert S. McNamara urged Tuesday that President Bush heed a lesson from Vietnam and not go to war with Iraq without prior public approval. A Republican senator agreed that "If we start having body bags coming back, we will have a very serious revolt."

McNamara, who was Lyndon B. Johnson's defense secretary at the height of U.S. involvement in Vietnam, told the Senate Foreign Relations Committee the administration should continue to rely upon economic sanctions as the main weapon against Iraq for a year or more.McNamara, meanwhile, asked the Senate committee: "Who can doubt that a year of blockade will be cheaper than a week of war?"

Asked to compare the situation with Vietnam, McNamara said: "I do not believe the president should - and I do not believe he will - initiate action without the approval of the American people expressed by the approval of the Congress."

He said those who focus on the costs of a prolonged embargo fail to see the costs of immediate military action.

"If we carry on sanctions for 12 to 18 months, there's no question we risk fracturing the unity of the international coalition" lined up against Iraq, he said.

"But I can tell you, it's hardly a risk - it's almost a certainty - that if we undertake military action there will be a fracture of the unity . . .

"There are divisive forces in the Arab world. They are going to be fed by the initiation of military action that is going to appear to many in the Arab world to be the unilateral action of the United States.

"It is a far lesser risk than the loss of thousands of American lives."