President Bush had an opportunity in his State of the Union message to level with the public about the probable costs of the Persian Gulf war and to ask for appropriate sacrifices. He did neither because he is still placing all his bets on a short, swift war that can be supplied out of existing inventories with minimal loss of lives.

The nation, including those who think that Bush entered the war prematurely, fervently hopes the president is right. But Saddam Hussein may not cooperate in making it a short war, and the president ducks his responsibilities when he fails to point that out.

In his address to Congress, Bush gave only minimal attention to the need for a serious energy program that would diminish America's excessive consumption of oil and dependence on imports. He mouthed the same generalities we have heard from every president since Nixon.

But why not a gasoline tax to do double duty -- to cut consumption and raise revenue? Why not, if Bush isn't ready for a Persian Gulf surtax, a Persian Gulf War Bond campaign to involve a public untouched except for its volunteer armed forces and their families?

To be sure, money pales against the price to be paid in human lives. But the administration has an obligation to provide sober estimates of financial costs of war based on a range of real-life scenarios.

America can and will sustain whatever the price turns out to be, but we should have learned from the Vietnam experience that the worst public policy is to underestimate true costs and then delay paying the bills.

Neither Bush nor the Department of Defense has given Congress any accounting of actual expenditures so far nor any official estimate of what the war could ultimately cost. On "Face the Nation" last weekend, Budget Director Richard Darman said most of the cost of a 60-day war would be covered by contributions from our allies, leaving American taxpayers to pick up a piddling $15 billion check, less than a couple of good-sized S&L bailouts. If you buy that scenario, I've got a nice bridge over San Francisco Bay I can sell you cheap.

Military officials privately concede that unless Bush backs off his commitment to push Saddam out of Kuwait, this is going to be a longer war than originally planned, measured in months -- not in weeks or days.

Therefore, as noted by Walter S. Mossberg in The Wall Street Journal, there is likely to be a need for replenishing the existing inventory of high-tech weapons such as the now-famous Patriot missiles. A military planner tells The Post's George C. Wilson: "Some nights, we use up a full day's production of Patriot missiles on one Scud."

Other unplanned contingencies crop up. Belatedly, we learn that enemy troops hide from allied aircraft in high-quality bunkers, built by European Community manufacturers to NATO standards. So one parallel with Vietnam looks ominous: Saddam has made sure he can exact huge American casualties in a land war. The Congressional Budget Office puts the number as high as 45,000.

Then, the allied high command was surprised by Saddam's outrageous and ecologically disastrous oil spill into the Persian Gulf -- proving that his determination to fight the "infidel" will take its own special toll. The president can rightly be angry about Saddam's devilish decision to pollute the Gulf, but Bush's first reaction that it conforms to no military doctrine was naive.

No one knows the price of the ecological rehabilitation of the Gulf, but it's bound to be enormous. Clearly, the oil spill, like the Scud attacks on Israel and Saudi Arabia (the eight-day cost to Israeli GNP, $400 million), are shrewd tactical blows calculated to divert and waste allied resources. If not contained, the oil spill could affect Saudi refinery operations that supply fuel for allied tanks and aircraft.

What are the ultimate dollar costs of the war and its aftermath likely to be? No one can say for sure. The Congressional Budget Office guesses that a war lasting "months" -- anywhere from one to six -- would add $86 billion to the budget deficit. Darman's "Face the Nation" estimate was based on $500 million a day, or $15 billion a month. But suppose the cost runs higher -- and longer? Can we really expect our allies, apart from Saudi Arabia and Kuwait, to continue to finance the largest share of the cost?

There are other uncertainties in assessing the eventual bill for the American taxpayer, including Soviet aggression in the Baltic states. That puts in limbo the Department of Defense's plan for a major reduction in military forces.

And who knows the price tag for postwar rewards to our allies? By turning the other cheek when China sentenced Tiananmen Square protesters, we may have paid off Beijing without new cash. But we will be presented with huge bills for reconstruction and loss of income from Israel, Egypt, Turkey, Syria and -- if King Hussein manages to switch to the right side in time -- from Jordan.