The bipartisan budget deficit deal between President Reagan and Congress is supposed to be phase one of a grand plan to restore the confidence of financial markets, shaken by Black Monday, Oct. 19.

Phase two is to be a new meeting, to take place soon, among the finance ministers and central bankers of the seven major industrial powers to regenerate economic cooperation and stabilize exchange rates.

But Treasury Secretary James A. Baker III and his opposite numbers in the six other nations face a dilemma as they make preparations for that G-7 meeting. Can they pull off a deal that is credible if they set stabilization of the dollar as a major goal?

The last time the major powers met, it was at the Louvre Palace in Paris in February. There -- with advance publicity and expectations rising just as high as they are now -- the ministers and central bankers undertook to stabilize exchange rates "around {then} current levels."

But the now famous (notorious?) Louvre Accord didn't hold. After eight months, it collapsed altogether: the stock market crashed, after which Baker admitted that if the United States had to choose between its commitments at the Louvre to hold the dollar steady, and a recession at home, it would let the dollar fall.

Now, as the nations head for a "Louvre II," pressures are reasserting themselves for yet another agreement to stabilize currencies at around present levels -- which are, of course, down from Louvre I.

All of America's partners -- but especially West Germany, Japan and Britain -- want to be assured that the dollar will fall no further. If it does, it puts a crimp in their export business. "A sharp further fall in the dollar is not merely wholly unnecessary, it would be harmful to all concerned," said British Chancellor of the Exchequer Nigel Lawson.

Without a genuine commitment to stabilize exchange rates, "there would be little point in holding a G-7 meeting at all," Lawson warned.

But many economists worry that in its anxiety to convey a sense of stability to the financial markets, the G-7 may once again be writing a contract it can't fulfill. "Their credibility is so damaged from the previous meeting that another premature agreement to stabilize rates could be devastating," says C. Fred Bergsten, director of the Institute for International Economics.

European and Japanese leaders, more concerned with symbolism than substance, have welcomed the Reagan/Congress budget deal because it permits the G-7 process to resume. Ironically, the European and Japanese officials have been more optimistic about the accord than are many of the American negotiators who took part in the process, and other observers.

A specially convened two-day meeting among international economists at Bergsten's institute last week concluded unanimously that -- at best -- the bipartisan deal will level off the American budget deficit at about $150 billion a year for the next two years.

"That's not good enough" to improve underlying conditions, Bergsten says. In other words, little relief should be expected from the underlying conditions that place the economy at risk, including the oppressive American trade and current account deficit.

The bipartisan leadership's excuse for not producing a better deficit package was that it didn't feel as much pressure from Main Street as from Wall Street: The real economy, the leadership says, is not all that bad. Economic growth is rolling along at a 4 percent rate, unemployment isn't too high, inflation is under control, the Dow Jones index has recovered from the lows.

I asked one of the negotiators -- House Majority Leader Thomas S. Foley (D-Wash.), who defends the package as the best bipartisan deal that was possible -- what would have happened if the Dow Jones industrials had plunged 200 points during the last few days of the negotiations. His answer: It would have speeded action on the agreement, but would not have changed the size or the composition of the package significantly.

Nonetheless, Foley admitted that next year, because of a combination of lost revenues (because of the Tax Reform Act of 1986), and potential adverse economic conditions, as much as $25 billion of the $46 billion budget savings projected could disappear.

With that as background, then, the operative questions are these:

Is it possible for the G-7 to put together a meaningful agreement that the public and financial markets will take seriously? And if they do, how long will the honeymoon last?

Assuming that Congress at least delivers by Dec. 16 all that the White House and congressional team promised (that's probable, but not an absolute certainty), the optimum result from a new G-7 meeting would include:

A solid commitment by West Germany to expand its economy, enabling Western Europe to speed its recovery. The dean of German economists, Herbert Giersch of the Kiel Institute for World Economy, told the Bergsten meeting that the Kohl government must accelerate its tax cut package and undertake other stimulative measures, including lower interest rates, to soak up unused and underused resources.

A commitment by Japan to continue the expansion program already under way for four to five years.

An American willingness to reduce interest rates -- if its partners agree -- along with a firm antiprotectionist policy to supplement the budget deficit steps.

And how about exchange rates? That is the tough issue. It would make sense to use language that avoids the trap of -- once again -- stabilizing the dollar at a level that the exchange markets won't buy. Bergsten's suggestion: a promise to stabilize rates not "at current levels," but within a wide range -- say 10 percent on either side of the levels prevailing when the deal is signed.

Those would be fairly realistic commitments. The West Germans should be worrying, not only about the drop in their own stock market but about the stagnation in their real economy. Japan has been able to prove to itself that it has been able to live with "endaka" -- the higher yen -- and could probably endure a rate of 120 yen to the dollar, which would represent another 10 percent appreciation.

For the United States, the big test may come next year as work begins on the fiscal 1989 budget. The negotiators came up with the minimal package this time. The markets may force them to work harder next year -- and remember, next year will be a presidential election year