The United States and its six major trading partners yesterday called for a halt in the decline of the dollar, pledging increased -- but unspecified -- cooperation to prevent the American currency from falling below the exchange rates prevailing worldwide at 11 p.m. last night, when their communique was released.

They also said they would act to keep the dollar from rising too high -- in effect establishing a new "target zone," the low point of which are the 11 p.m. quotations, with an unknown upper end. The announcement is "in lieu" of a new meeting by the Group of Seven economic powers, a senior Reagan administration official said.

In general, the nations promised to maintain more stable exchange rates, which they said is in "their common interest," and to "cooperate closely on exchange markets," a transparent commitment that their central banks would intervene to try to prevent "excessive fluctuation" in exchange rates by buying and selling currencies.

"The process of policy coordination is alive and well," the administration official said. But the seven nations -- the United States, Japan, West Germany, France, Britain, Italy and Canada -- outlined no new actions to support their intention to stabilize exchange rates. The communique was issued simultaneously in all seven capitals.

As news of the statement leaked into the Tokyo market this morning, the dollar temporarily dipped below 126 yen from a Tokyo opening of 126.65 yen as speculators concluded that the G-7 had produced nothing new in efforts to stop the currency falling, Reuter reported. The dollar later recovered to just over 126 yen after the statement was formally unveiled.

A key question unanswered by the communique is whether the agreement can be carried out without further policy action by the United States, such as an increase in interest rates to make the dollar more attractive to foreigners. The administration official who briefed reporters yesterday refused to answer questions about the future course of interest rates.

The official also said that the United States opposed issuance of bonds denominated in foreign currencies, which would transfer to the United States the exchange rate risk for those making investments in U.S securities. "We have adequate reserves to cooperate with other members of the G-7 {without issuance of such bonds}," the official said.

Last night's pledge to stop the fall of the dollar represents a reversal of American policy that had prevailed since just prior to the Oct. 19 stock market plunge, when Treasury Secretary James A. Baker III declared that the United States would not raise rates to keep the dollar from falling. Following the market's collapse, Baker said that the nation's first economic priority was to avert a threatened recession by following an easier monetary policy.

The statement had been anticipated by financial markets following the conclusion of U.S. budget deficit reduction efforts yesterday. But a pledge to try to defend the dollar at a precise level had not been expected.

The senior administration official said last night that the detailed communique, along with an annex outlining major policy actions taken since a meeting of the Group of Seven economic powers last February, would take the place of a new G-7 meeting, which had been discussed among the finance ministers after Oct. 19 as a way of restoring confidence in financial markets.

He expressed satisfaction with actions taken by U.S. economic partners to expand their economies, and predicted that the U.S. trade deficit would decline in money as well as volume terms.

The key and last paragraph of an eight-paragraph communique said not only that "a further decline of the dollar ... could be counter-productive" for the world economy by damaging growth prospects, but also that "a rise in the dollar to an extent that becomes destabilizing" would be unacceptable.

The official would not say by how much the dollar would have to rise before the G-7 would take actions designed to bring it down, but noted that "there is an explicit understanding {on that} among some of us." Later, he said that the explicit understanding to keep the dollar from again rising too high is shared "among all" of the finance ministers.

Baker's earlier refusal to say that the dollar had fallen enough was perceived by financial markets as the equivalent of a positive policy to pursue further dollar weakness. Even a mid-November statement by President Reagan that the U.S. was not seeking a further decline did not end the slide.

But officials said yesterday's communique is intended to establish a new understanding among the seven partners that restores exchange rate stability as a critical priority and reaffirms the basic objectives on coordination that had been undertaken at the Louvre Palace on Feb. 22.

The senior official said he was "optimistic" that the new agreement would be more durable than the Louvre Accord -- which had promised to "foster stability of exchange rates" around then-current levels -- because the dollar had since declined to presumably more realistic levels, and because the United States, West Germany and other nations had since taken actions, especially since the October collapse, designed to correct trade imbalances.

At the close of trading in New York yesterday, the dollar was worth a bit less than 127 yen, down about 17.5 percent from 154 yen, and just under 1.63 German marks, down 11.4 percent from 1.84 marks at the time of the Louvre agreement.

Yesterday's communique conceded that the collapse "may have some adverse effects" on the economic growth in the industrialized world. But a senior administration official said that a recession is now not considered likely.

The American policy of letting the dollar drift downward, despite the Louvre Accord, had been resisted by America's partners, especially West Germany and Japan, and sometimes bitterly. German officials as recently as yesterday blamed a weakening of their economy and a reduced growth forecast on the sharply higher German mark.

Last night, administration officials refused to answer any questions on the future of U.S. monetary policy, or on plans to intervene in exchange markets to achieve the stability of exchange rates that they now say is in "their common interest."

But intervention is strongly implied in the text of the communique, which adds: "The ministers and governors stressed the need for consistent and mutually supportive policies, and believe that the measures being taken will accelerate progress towards the increased, more balanced economic growth, and sustainable external positions necessary for greater exchange rate stability."

Although the official would not acknowledge that the new accord, worked out largely by telephone, established an acceptable range for the dollar, he admitted that the language of the communique set an explicit floor for the dollar -- the ll p.m. levels of last night -- and an unstated upper limit.

Once again, the G-7 partners implored the newly industrializing countries (NICs) that run large trade surpluses to take actions that will help reduce global imbalances.