Sen. William S. Cohen returned from the Persian Gulf this week with a sobering thought for the American public, sage advice for President George Bush, and political reality therapy for the Soviet Union.

Congressmen and senators, utter failures on major domestic issues, have been lining up for flights to the front lines in Saudi Arabia, a distant flashpoint that has become a mecca for photo opportunities and a welcome diversion from the savings-and-loan and budget crises. Cohen went, but he brought back new perspectives that should serve as a springboard for national debate and action.

President Bush, he said, should seek the support of Congress, promptly, for the action in the Middle East. This is sound advice from the senator to the president. Although Mr. Bush is not yet obligated under the War Powers Act to obtain congressional consent to his decision to confront Saddam Hussein militarily, he would be wise to request that support now, while public opinion and events bolster his position.

The Soviet Union, the senator points out, cannot have it both ways. It cannot be both a responsible member of the international community and at the same time provide military aid to a dangerous dictator who has been declared an outlaw by the rest of the world.

It would be contrary to U.S. national interests to assist the Soviet Union in rebuilding its industry, in overcoming its agricultural problems or in stabilizing its domestic political situation while the U.S.S.R. props up an Iraqi regime that is threatening to cripple the U.S. economy by constricting the supply of oil.

For the American public, which is watching the full-time military establish a foothold in the desert while hometown people are called to active duty, the senator’s observations on the Gulf provide a striking and needed change of focus.

The initial military commitment in the Middle East was necessary to protect Western economic interests, and was appropriate to counter the threat posed by Iraq to the Saudi oil fields and to ensure the political integrity of that region, but the U.S. now is in jeopardy of bogging down in the sand.

The lack of executive-legislative consensus is dangerous politically. If the standoff in the Gulf drags on, and there are no clearly stated, long-term U.S. policies and objectives, national resolve and staying power will be undermined. Congressional support for the president’s action is an issue that the country should confront now.