IN AUTHORIZING military action against Iraq, the United Nations Security Council last week armed President Bush with the international equivalent of the Tonkin Gulf resolution that Lyndon Johnson employed to legitimize an open-ended war against North Vietnam. This is only one of many worrisome parallels between the Persian Gulf crisis and the conflict in Southeast Asia, despite Bush's vow in his Friday television statement not to put the nation through another Vietnam.

No matter what happens next in the Persian Gulf, war or no war, Bush in the opening steps of the crisis, like Johnson 26 years ago, has sown seeds that may bear bitter fruit for him -- and the country -- in the years ahead. In emulating Johnson by rounding up a huge American expeditionary force and, with little congressional participation, sending it to a distant troublespot, Bush risks dealing a major blow to the very mission he seeks to carry out -- reaffirming the United States' role as global leader.

Even in dismissing the Vietnam parallel, Bush acknowledged it is much on his mind. Perhaps his look down that dark tunnel contributed to his decision to accompany his bellicose statement with an invitation to Iraq's foreign minister to discuss the situation with him and our gulf allies next week and to promise to send Secretary of State James Baker to Baghdad for talks with Iraqi leader Saddam Hussein. In any case, the president was almost surely shaken by testimony earlier last week by two former chairmen of the Joint Chiefs of Staff, Adm. William J. Crowe Jr. and Gen. David C. Jones, as well former National Security Agency director Lt. Gen. William E. Odom, who strongly counseled caution and patience in the desert.

Of course, if things go well in the gulf the president would be immeasurably strengthened. If, as Bush said he hopes, Saddam responds to his heightened message of commitment by withdrawing his troops from Kuwait before shooting or bombing starts, the president's high-stakes strategy will have paid off. But if, despite the president's assurances, the gulf confrontation slows to an unresolved stalemate, or worse, becomes a bloody standoff, Bush's ex-post-facto justifications for Operation Desert Shield will not quell the political storm certain to rise at home. And the chances of mobilizing a national consensus behind any future strategic interventions by the United States could be undermined long into the future.

Many of Bush's potential troubles stem from following LBJ's handbook, which could be entitled "How to Go to War Without Anybody Knowing It Until Too Late." Both Johnson and Bush treated Congress like a doormat, getting lawmakers aboard early on by not saying how big a war they were prepared to fight. And Congress, despite its constitutional war-making power, obliged, at least initially.

Although Bush said he would welcome a congressional resolution "enthusiastically endorsing" the U.N. resolution, he made it clear that he would not welcome a wide-open debate among the "endless experts" on Capitol Hill. And even if Congress does return to debate an authorization of the use of force, it could find it virtually impossible to vote down such a resolution, since the commander-in-chief already has engaged U.S. forces in a massive face-off with Iraq. This is why the U.N. resolution to use force, and any similar congressional resolution, inevitably resemble the Tonkin Gulf resolution: They can provide a legal framework for a conflict of unknown dimensions, but they fall short of a national referendum on whether hundreds of thousands of troops should be sent into battle.

"It is interesting that two presidents, one using draftees and the other reservists, committed a force of more than 400,000 troops without Congress playing its traditional role," said Martin Binkin, a manpower specialist at the Brookings Institution. A closer look shows how this happened first in Vietnam and now in the Persian Gulf. The lawmakers who voted, almost unanimously, for the Tonkin Gulf resolution on Aug. 7, 1964 thought they were doing little more than agreeing that Johnson should protect American boys already in the Vietnam theater -- especially the crews of the two destroyers which the Pentagon said had been attacked by North Vietnamese torpedo boats. There was no suggestion from Johnson or anyone else that in passing the resolution Congress was endorsing an open-ended war. At the time, only 16,500 U.S. military personnel were in Vietnam. By 1968, when the Senate Foreign Relations Committee finally opened televised hearings to examine how Johnson had taken the country so far into a massive conflict, the United States had 500,000 service personnel fighting the war.

Bush, like Johnson before him, has managed to keep Congress and the public out of the crucial decision process until after he committed almost as big a force to the Persian Gulf as Johnson sent to Vietnam. While the president sought international support early on, the U.N. authorized force after, not before, U.S. and allied troops had been sent to the gulf. And whatever follow-up resolutions Congress passes cannot change the fact that Bush has "Johnsoned" them. The lawmakers, once again, can do little more than look back in anger -- American boys are already committed in huge numbers.

Administration officials made headlines in August by saying the U.S. deployment to the gulf could be as high as 50,000. Today the force numbers 240,000. Next month it is projected to soar to more than 400,000. The politicians back home have no choice but to give these forces what they need, whether they remain in Saudia Arabia to keep Iraq from invading that country -- Bush's original rationale for the deployment -- or take military steps to strip away Saddam's military power -- the later rationale.

Bush's installment-plan revelations may have been driven by various reasons: concern about tipping off Saddam; lack of a master plan for pursuing the confrontation; or desire to avoid stirring up opposition. Johnson was more candid, admitting early in the Vietnam buildup that he did not want to let the American people in on his real plans. "I'm bringing 'em along," he told a visiting editor. He said he was purposely behaving like a passionate suitor in the front parlor with his girlfriend: "You got to slide your hand slowly from her ankle toward her knee to get where you want to go, else you'll get your face slapped."

Both Johnson and Bush drew forces from the active duty military in their first phases of deployment but soon found this would not be enough manpower for carrying out their unrevealed master plans.

In the Vietnam buildup, the Pentagon chiefs recommended activating reservists. Johnson decided this would be too provocative politically and too disruptive economically. He raised draft calls, which put most of the burden of Vietnam on the country's have-nots, who could not escape through college deferments and knew little about other dodges. The draft, of course, became so unpopular that President Nixon got rid of it in 1973 and formed the all-volunteer force now in existence.

As a result, Bush did not have a draft in place to augment an active-duty military force that is much too small to provide 400,000 people for gulf duty. It is virtually impossible for the Army and Air Force of the 1990s to go to war without activating reservists, because so much of the combat-support mission has been lodged in those units. {See story above.} The president applauded the currently high morale of U.S. troops in the gulf. What he did not point out is that the thousands of troops now in the desert were recruited on a very different idea of why they were serving. Since Vietnam, military recruiters have sought to make active military duty attractive by portraying service as a way for young men and women to experience adventure, save money for college or learn a trade. Killing and getting killed is not in the television ads or on the posters. Bush, like Johnson during the Vietnam War, is still groping for a rallying cry to get teenagers and their parents to believe it is worth risking their lives to free Kuwait, save gulf oil or topple Saddam.

"We don't have a volunteer army, we have a recruitment army," lamented one colonel last week. And recruiters, blaming fears about getting killed in the gulf, report increasing difficulty in signing up young men. The Army, for example, signed up 32 percent fewer males during November than it had projected before the gulf crisis.

Sen. William S. Cohen (R-Maine), ranking Republican on the Senate Armed Services force-projection subcommittee, said he anticipated the political and public dissent that is now building over Bush's threats to go to war. "I argued {without success}," Cohen said in discussing meetings with administration officials, "that the president would be much better off if he activated the War Powers Act at the beginning. This would get Congress aboard at the start and help unify the country."

Rep. Les Aspin (D-Wis.), chairman of the House Armed Services Committee, now feels that the political divisions over the president's gulf policies make it "no longer an option" for Bush to go to war without some kind of congressional vote supporting the action.

In interviews last week, military leaders involved with the gulf build-up expressed another concern. "If things go wrong down there," said one general who is a veteran of Vietnam, "it will be our fault again. We don't need that." Military leaders are very willing to follow the president's orders regarding the gulf commitment, but lament that many civilians believe they are issuing rather following orders.

Gen. Colin L. Powell, chairman of the Joint Chiefs of Staff, also a Vietnam veteran, is part of the "never-again" school, whose thinking was reflected in the president's assurance that "if one American soldier has to go into battle, that soldier will have enough force behind him to win and get out as soon as possible . . . ." Powell sought, and Bush agreed, that Americans fighting in the gulf should have every possible advantage in firepower and even in numbers at those places commanders might choose to attack.

Powell and his fellow chiefs would like the attackers-vs.-defenders ratio to be 3 to 1 at least at those points. Saddam now has a force of 450,000 in Kuwait and has threatened to add another 250,000. If Bush should try to match these added troops, he again faces uncomfortable parallels with Johnson, who eventually met with insurmountable political opposition to a wider U.S. presence in Vietnam. Like Vietnam, Desert Shield could become a major turning point for U.S. foreign policy in which the United States will either proceed further into the role of world-policeman or retreat to a narrower defense of its interests. Congress in writing the fiscal 1991 defense authorization directed the military to restructure itself so it could rush to global hot spots in time to influence the outcome of a crisis and still have the firepower to make a stand against modern forces elsewhere.

If Bush's Persian Gulf effort should end badly, it is likely that Congress will reverse itself and return to the posture it took in 1967 at the height of the Vietnam War. Back then, chairman Richard B. Russell (D-Georgia) of the Senate Armed Services Committee sank the Navy's plan for a fleet of floating warehouses called fast-deployment logistic (FDL) ships that would be kept near likely trouble spots. It was the kind of force-projection capability that has proved of crucial value in Desert Shield.

"We should not unilaterally assume the function of policing the world," Russell said in persuading the Senate to sink the Navy's FDL program. "If it is easy for us to go anywhere and do anything, we will always be going somewhere and doing something."

George Wilson has covered military affairs for The Washington Post for two decades.