This week's two-day congressional shoot-out on the administration's latest shrunken request for aid to the contras is the best example we've seen since, oh, let's say, Lebanon in 1983 of how badly the United States makes foreign policy when a divided government cannot even agree on ends, let alone means.

Operating in a legislative straitjacket negotiated between the administration and congressional leaders last year, the House will vote up or down (no amendments allowed) tomorrow. The Senate will do the same the next day. But an adverse House vote would be enough to kill the measure whatever the Senate does.

Then what? Apocalypse now, if you buy the live-or-die, now-or-never hysteria that has been the hallmark of the administration's case at almost every step along the way in its campaign for aid to the Nicaraguan resistance forces over the years. Nicaragua will become ''a base camp for the Soviets in this hemisphere,'' says President Reagan. Never to be outdone, the assistant secretary of state for this hemisphere, Elliott Abrams, told ABC: ''If we lose this vote and abandon the freedom fighters, I think that we're only a few years away from Soviet domination of this region between Mexico and the Panama Canal.''

That's baloney. Even when allowance is made for Abrams' role as designated hit man for contra aid, it makes no sense. The administration insists, on the one hand, that the Sandinistas are dedicated Leninists, thoroughly untrustworthy and hell-bent on conquest of Central America. On the other hand, they are under ''incredibly large economic and military pressure,'' says Abrams, and with ''a little bit more aid for the resistance'' they can be made to ''back off'' from their evil ways.

The administration's deep-down desire comes through loud and clear. If the Sandinistas are every bit as bad as they are cracked up to be, nothing less than their removal would serve administration purposes. But the idea that this could be achieved by ''a little bit more aid for the resistance'' is belied by a look at what the administration thought was needed only a few months ago -- and at what it is begging for now.

Last October, President Reagan was pledging ''full democracy'' for communist Nicaragua. (What else could that mean but overthrowing the Sandinista regime?) He was telling a meeting of the Organization of American States he would ''fight for'' an 18-month, $270 million contra-aid program ''as long as there's a breath in this body.'' He was talking about $15 million a month, most of it in arms, clear into the early months of the next presidency.

By November, Reagan had thrown in the towel. In the end, Congress put the contras on what amounted to a dole: $3.5 million, then $3.2 million and finally another $14 million to last until the end of February. This was ''humanitarian'' or ''nonlethal'' aid (including helicopters and other transport for supplies such as food, clothing, medicine).

Early this year, there was brave talk of a resumption of military as well as ''nonlethal'' aid to the tune of as much as $100 million or more. By last week the administration had retreated to a mere $36 million for the next five months -- with only a piddling $3.6 million in military aid. Even this would be held in escrow until March 31 and released only if the Sandinistas and contras fail to reach agreement on the cease-fire required under the terms of the five-nation (Costa Rica, Guatemala, Honduras, El Salvador and Nicaragua) Central American peace plan.

The administration would have us believe that failure to approve this short-term pittance will take all the pressure off the Sandinistas to negotiate. The United States then would be helpless to influence events. Democratic leaders in Congress argue just the opposite: given the peace plan's strictures against all outside aid to regional insurgencies, approval of any new contra aid would provide the Sandinistas with an easy excuse not to negotiate. But the consequences, ironically, would be much the same: the United States would be equally hard put to influence events.

That there is something to be said for the arguments on both sides only makes matters worse. What it says is that it may not be all that important who wins. Either way, for lack of a nonpartisan consensus on what we're after in Nicaragua -- the overthrow of a communist regime, or its containment, or something in between -- this week's congressional voting on contra aid is likely to do no more than reemphasize U.S. irrelevance and prolong the agony. Ambivalence will be the winner. The Nicaraguan people will lose.