You had thought "Contadora" provided a possible way out of the Central America box? This was the week in which it dawned on the main body of conservative troops in Washington that Contadora may put us into a box. From being a diplomatic initiative that many liberals feared would fail, it has become for these conservatives an initiative they fear will succeed.

A month ago in Panama, the Latin states of the Contadora group tried and failed to bring Nicaragua aboard their effort to complete a regional peace treaty quickly, in order to provide a feasible live alternative to the war. The Reagan administration took some grim satisfaction in the Sandinistas' defiance of their fellow Latins and offered the conclusion that support of the contras was now the only way.

The Latins, however, would not take the Sandinistas' no for an answer. They have worked on Managua, and it now becomes possible, though far from assured, that the Nicaraguans will give some form of assent to a peace treaty by the Contadora deadline of early June. This will allow congressional opponents of contra aid to argue that there may be an alternative to a wider war after all. This argument, in the close political circumstances now existing, could tip the vote against aid.

This was always in the cards, and some conservatives, the State Department's Elliott Abrams for one, knew it. Negotiation means compromise: Contadora always meant getting gains in regional security in return for giving the Sandinistas a lease on political life. Abrams always thought that it was necessary to change the regime in Managua -- that only by democratization, worthy in its own right, could security be ensured.

But the notion that negotiation means settling for less than might be gained in a full military victory has come more slowly to others in Washington. Take the congressional Republicans who expressed their alarm about a supposedly imminent sellout of the contras to the president this week. Their villain is Philip Habib, the retired diplomat whom President Reagan was forced to name as his Central American envoy to show Congress he was serious about diplomacy.

Habib is a guy with a lot of scars, and when he was named, some skeptics swore up and down that he was going into the tank, and not for the first time, for President Reagan. Others, wondering if Habib had a bit of personal redemption in mind after his last scarring -- in Lebanon -- saw him as a useful new player in the game, arriving at a moment when both the Latin and congressional dynamics were in some flux.

To Habib, at any rate, is attributed an ostensibly new administration commitment to cut off the contras if Nicaragua accepts a Contadora treaty. This is what has the right wing moaning about "mixed signals" and "sellout." But it's all a bit odd. The reported new commitment is not new and is not much of a commitment: in the past as now, officials from the president on down have offered to support Contadora but conditionally, depending on whether Nicaragua was thought to be playing fair. Lots of room there. The conservative critics of Habib are getting a bit too absorbed by the fine print. What counts is what is in Reagan's head, and that appears to be the same familiar urge to roll back communism in Central America.

Still, the critics are on to something, though they are late in getting there. In the minds of some of the diplomats the idea persists that you need pressure and a safety valve, the contras and Contadora, and that you can play subtly between them. This is the classical approach to negotiations and, in one pair of skilled hands, it might work here.

In fact, the two elements are in two pairs of hands: the administration is applying the pressure, and Congress or some part of it is trying to open a safety valve. Far from there being coordination, there is a tug of war. I don't pretend to know what Phil Habib is up to, but any effort to create a usable diplomatic space for Ronald Reagan is bound to be an uphill job on the Washington end.

On the Nicaragua end, things are tough too. The Sandinistas are still arguing among themselves whether Contadora is a useful opportunity for tactical respite or a trap designed to disarm them. Managua's "left wing," like Washington's right wing, harbors a deep certainty that it faces a clever and devious adversary who will exploit its first hint of readiness for diplomatic compromise. In Managua, however, there doesn't seem to be a Phil Habib.