The dollar continued on a downward path last week, carrying the uneasy hopes of American manufacturers whose recovery depends on its decline.

President Reagan's approval of a U.S.-led campaign to lower the dollar's value prompted gratitude and frustration on the part of at least one business leader and supporter of the president, Edmund T. Pratt Jr., chairman of Pfizer Inc., a major pharmaceutical manufacturer and exporter: gratitude because the move was made; frustration because it was long in coming and because the dollar still has so far to go, in Pratt's view.

"I strongly support the Reagan administration. If I didn't, I wouldn't be serving in the positions I do . . . ," said Pratt, chairman of the administration's Committee on Trade Negotiations. But he and other members of the Business Roundtable, leaders of the biggest corporations, have grown hoarse pleading for action on the dollar, Pratt said in an interview last week.

"The Roundtable has been beating on the door of the administration for two and a half or three years on the strength of the dollar, and in general, we've gotten nowhere. We've gotten no response at all. Most of the administration has told us there is no such thing as an imbalance of the dollar -- it's a free market and whatever there is, there is. We've been greatly disappointed in the response of the administration to the dollar. . . .

"There are probably some in the administration who don't want the dollar to get weaker, even though it's killing manufacturing.

"If the dollar suddenly changed by 20 percent or more, those goods coming in from Japan will be less attractive, but they aren't going to give up those markets . . . All these things will help, and over the long term they must be done, but they won't solve the problem quickly," Pratt said.

Pratt was among several executives and economists speaking in different forums last week who said that the administration's efforts to reduce the value of the dollar were helpful -- but no substitute for either a real trade policy or actions to reduce the federal budget deficit.

Allen Sinai, chief economist for Shearson Lehman Brothers, said at a conference in Chicago that the price effects of a declining dollar will take a long time to work through the economy. Until then, any improvements in net exports will come from the reduction of income growth, which will cool demand for imports, more than from the change in the dollar.

C. Fred Bergsten, director of the Institute for International Economics, told a House subcommittee last week that he was encouraged by the early reaction of the dollar to the actions of the United States and the four other industrialized nations. In the week after the policy was announced Sept. 22, the dollar dropped about 5 percent overall and 10 percent compared with the yen. Every percentage point that the yen gains against the dollar eventually should reduce the U.S. trade deficit with Japan by about $1 billion, Bergsten said.

But he cautioned that, even with the declines in the dollar that began last February, the dollar is still only 2 to 4 percent below the 1984 average. "We are still on a path of steadily rising current account deficits, which could reach about $250 billion by 1990," he said. The current account deficit is the broadest measure of trade in goods and services. The decline in the dollar this year should lower that end-of-decade deficit by about $50 billion, but obviously leaves a long way to go, he said.

Sinai said he now thinks the trade deficit this year will be about $130 billion, not the $150 billion everyone expected.

"We have bought time by these measures" to lower the dollar, Robert Z. Lawrence said. The agreement by the five industrialized nations to act to lower the value of the dollar stilled those who would have voted for protectionist legislation in an effort to get the president's attention but who really had no strong desire for such legislation, he said.

Lawrence, a senior fellow at the Brookings Institution, said that, up until the agreement, the Reagan administration had ignored sectoral and regional needs brought about by the trade problem. Now the administration has acknowledged that there is a problem, Lawrence said.

Sinai said that the agreement was "95 percent a political move by an administration in trouble. They're in trouble on protectionism. They were losing that particular battle" when they decided to try to push down the dollar.

Leonard E. Santos, international trade counsel to the Senate Finance Committee, said he doesn't believe that Congress will end up passing much protectionist legislation. But if the economy turns sour and unemployment rises, "then pressure will intensify to do something, even if it's not very smart," he said.

Lawrence also said that the longer the delay in acting to reduce the federal budget deficit, the more it will hurt manufacturing. With the dollar declining, Lawrence said he sees a period of economic growth in the medium term for the manufacturing sector. Manufacturing will continue to shrink in its relative importance to the economy, but it will enjoy an absolute increase in growth through the end of the decade.

Lawrence said he doesn't expect any major reverses in the downward trend of the dollar. So far as Japan is concerned, Lawrence said he doesn't expect the yen to depreciate, at least not before Reagan is scheduled to meet with Japanese Prime Minister Yasuhiro Nakasone this month. In fact, Larence predicted a strengthening of the yen over the next few months.

Meanwhile, there will be numerous tests of the European currencies. Unless there are major policy moves, the additional decline in the dollar against most European currencies will be slight, Lawrence said.

Sinai said he doesn't know if the dollar will rise again, because there is no indication that the countries involved will change any of their fiscal or monetary policies. When asked whether he thought the move to push down the dollar would affect business planning, Sinai said that the traded-goods sector of the manufacturing industry should be over the worst and now can get back to planning.

Gordon added that a decline in the dollar may not affect trade very much because foreign exporters have set up distribution networks here and are trying to maintain a market share.

Lawrence said that there will be a slower-than-expected change in the net-export picture because there will be little price effect on imports until the dollar moves to much lower ranges.

"In exasperation, you hear the phrase said in industry: What this boils down to is the American government doesn't have a trade policy," Pratt said.

"The numbers scare me to death," he added. "A $150 billion balance-of-payments deficit year after year -- I don't think we can stand another year . . . The administration obviously thinks we can tolerate these numbers for awhile."