High British officials fear that Washington underestimates the potentially dangerous consequences for the West's economy of a fast-moving German-French monetary plan.

In private, they acknowledge that Prime Minister James Callaghan's government has been caught off balance by the speed with which German Chancellor Helmut Schmidt and French President Valery Giscard d'Estaing are fastening their scheme on major European economies.

Unless the paris-Bonn proposal to fix exchange rates is sharply modified, British officials fear it will serve to depress output and jobs not only in Britain but the U.S. as well.

Yesterday in Parliament, Callaghan tried to calm the storm that has publicly broken here over Britain's division with its chief common market partners. He told Parliament he and other leaders of the NINE held "a constructive meeting" on the plan last week in Bremen and acknowledged only that "there was some hard talking because we were getting to grips with important problems."

Callaghan repeated his view that "a zone of monetary stability in Europe was highly desirable." But he assured critical MP's he wanted to see "the details fully worked out" before Britain makes any commitment to the German-French plan.

So far as is known here, the Carter administration has said only that it has "no objections in principle" to a scheme for a European monetary unity. In the London view, this is an astonishingly bland response, a failure to recognize how quickly events with profound consequences are moving.

Key aides known for their restrained understatement are privately warning that the plan now being prepared could serve German exporters, impart the economic discipline Giscard now wants to impose on the French but give Britain and the U.S. an uncomfortable choice between deflating their economics or falling currencies.

The Common Market's bureaucratic apparatus, led by President Roy Jenkins, is throwing its weight behind the plan in the belief that it will finally give the Brussels machinery the power it has sought since its birth a generation ago.

Callaghan's own words are partly responsible for his government's latest discomfort. For months, he and some of his cabinet have been saying that the present international money system - floating exchange rates, fixed largely by demand and supply and partly by the management of central banks - has held back the economic advance of the West. Currency [WORD ILLEGIBLE] , it was said, created uncertainty that discouraged business investment, output and employment.

The communique that emerged from the Common Market summit in Bremen Friday barely mentions any responsibility for countries like Germany with big surpluses in their balance of payments. It urges them only to follow a policy of "stability at home and abroad."

In British Eyes, this is sinister. To London, it looks as if Paris and Bonn are placing all the stress on stability and ignoring growth. That frightens London and, high officials insist, should worry Washington as well.

The British, of course, cann't be forced to join. But Paris and Bonn could go ahead on their own, probably with the other countries now tied to the mark zone - Belgium, Luxembourg, Holland, Denmark and Norway.

The great monetary speculators - banks, multinational corporations, Arab and other foreign governments - might view the Pound as a naked and vulnerable currency. They would be tempted to sell, forcing the Pound down, increasing British inflation.

"It is very hard to be tail-end Charlie in this kind of game," one top aide said grimly.

If Britain joined, it might be under constant pressure to cut its output and imports to stay inside the fixed rate band. That is an equally unappetizing prospect.

The U.S., says London, could suffer too. Germany would gain new allies in its effort to prevent the mark from rising against the dollar. That would enable Bonn to increase its food of exports to the U.S.

The U.S., like Britain, could then restore a balance either by letting the dollar fall further or by squeezing its own economy until imports shrank.

Any fall in the dollar, moreover, would not merely be limited to countries with whom the U.S. was in deficit - like Germany - but all those grouped around the mark.