Ingersoll-Rand Co., a corporation that has competed successfully in the world markets since before World War I, finally hit a massive roadblock that is stalling even its heavy construction equipment: an overly strong dollar that costs orders for its made-in-America products.

It knows the high dollar is the culprit in lost sales because of a series of cost comparisons between identical products manufactured in its U.S. plants and in its less-efficient factories in Italy and Great Britain.

A rotary compressor, for instance, cost 64 percent less to make in Britain than in the United States. For five machines produced in the Italian factories, costs ranged from 60 to 87 percent of those of identical products made in the U.S.A.

"Notwithstanding the European plants' manufacturing disadvantage in terms of lower volume and less automation, their manufacturing costs in total are so much lower than the costs in the United States that we cannot compete against our own factories abroad," said George Liney, an Ingersoll-Rand executive familiar with the company's international operations.

"Unless the dollar weakens drastically and soon, it will not be long before we will supply the U.S. market with machines made abroad," he added.

That company is not alone in suffering from the effects of America's high dollar, which, according to a study by Sara Johnson of Data Resources Inc., is overvalued by about 34 percent in relation to the currencies of the United States' major trading partners.

Some of the best and most highly competitive American companies -- big and small alike -- complain that the strong dollar hurts their ability to compete in the world.

"American manufacturers are under the gun in terms of the dollar being so strong. It's an enormous competitive disadvantage from my point of view," said G. Vicary Mahler, president of Audiosears, a small, $5-million-a-year company that makes telecommunications equipment.

"Until the last three or four years, we never had problems with foreign competitors because of price," added Dennis Boerger, international sales manager of Minster Machine Co., an 88-year-old machine-tool maker.

"We have always been able to sell against competitors that were 15 percent to 20 percent less costly because of our good reputation. That was not a stumbling block for us. But 50 percent is," he said.

The overly strong dollar costs U.S. business profits and American workers jobs. More significant, it threatens to undermine America's ability to compete in world markets for years to come.

The high dollar, moreover, has opened the U.S. market to a flood of low-cost imports and is blamed by President Reagan's Council of Economic Advisers for about half of the merchandise trade deficit, expected to reach a record $130 billion this year. And it has robbed U.S. industries of many of the fruits of the strong economic recovery, as a major share of the boom in capital goods purchases by American companies has gone overseas.

"U.S. companies are participating in the growth, but they have lost market share and are not participating equally," said the U.S. Commerce Department's senior international economist, David Lund.

Even the most highly competitive American industries -- capital-goods manufacturers and high-technology companies -- suffer from the overly high dollar, according to economists and business leaders.

"It's having a devastating effect on American industry, and I think it's going to get worse and worse," said C. Fred Bergsten, a former Carter administration Treasury official and director of the Institute for International Economics.

He estimates the U.S. trade deficit will reach as high as $200 billion or $250 billion for the rest of the decade unless the dollar is pulled down by about 35 percent.

The trade deficit meant the loss of about 2 1/2 million U.S. jobs to date, and that number is likely to double to 5 million by 1990, Bergsten said. There currently are 8.4 million unemployed. He acknowledges "modest offsets" in employment, largely in service industries, because the high level of cheap imports has dampened inflation.

"Despite over a year and a half of high rates of GNP gross national product growth, manufacturing employment by May 1984 was half a million below the 1981 level and still about the same as in 1970. All the net increase in employment since 1981 is in the service sector of the economy," noted Stephen Cooney, an economist in the international affairs division of the National Association of Manufacturers.

Lund, the Commerce Department expert, said the number of unemployed Americans has grown by about 307,000 during four years that encompass most of President Reagan's first term -- from September 1980, when the sharp rise of the dollar started, to last September.

The big losers are in goods-producing industries where American companies once held sway in the world -- such as machinery, down 208,000 jobs; fabricated metal products, down 83,000 jobs; and chemicals, down 38,000 jobs.

The big manufacturing winner was electronics, with 209,000 more jobs, but NAM economist Cooney notes that even that is eroding as imports of computers increased 50 percent in the first half of the year.

"The implication of those trade developments is that those who argue that the United States is shifting its focus from 'traditional' industrial sectors to 'hi-tech' industries are wrong," Cooney said.

"An overall U.S. trade surplus in such high-technology products of $27 billion in 1980 has dwindled in the first half of 1984; exports have shown only a slightly upward trend while imports have more than doubled.

"The same trend has affected capital goods in general, long the most competitive U.S. industrial economic sector," Cooney continued.

"By reducing the price of imports to Americans and making U.S. products more costly to foreign buyers, the dollar's appreciation has eroded the competitiveness of U.S. industry," said DRI's Johnson. "As a result, many U.S. companies are shifting production abroad to take advantage of lower labor costs; others are abandoning export markets or seeking import protection."

Lynn O. Michaels, chief economist for Weyerhaeuser Co., said the giant West Coast lumber firm has lowered export prices of some products, such as linerboards, below what it charges Americans to meet the foreign competition.

"We hate to abandon export markets because of what may be a temporary situation," he said. "A lot of companies are sustaining exports to purely maintain markets and not really for profits."

The high dollar poses a different problem for Deere & Co., a major maker of farm machinery. "The most significant aspect of the strong dollar is its impact on our customers, the American farmer," who finds his crops undersold on the world market, said the company's chief economist, Dean McKeen.

Commerce Secretary Malcolm Baldrige worries about the long-term effects of the high dollar on American businesses that are losing overseas sales.

The longer American companies are kept out of foreign markets because of the strong dollar, , the harder it will be for them to regain sales when the dollar drops in value, he pointed out. Foreign companies and governments will develop relations with new suppliers that are hard to break as they build up inventories of spare parts for the new equipment and arrange for modifications to fit their special needs.

"Even in the United States domestic market, it's tough once you have been out for a while," Baldrige said. "Clearly, there is a point where irreparable harm is done to a particular company, particularly in industries that are competing abroad."

As U.S. firms lose market shares in the world, moreover, future competitors develop as small companies become world-class competitors. "If this keeps on for very, very long, you will see a lot of Pacific Rim countries that will move from basic machines to more sophisticated versions," Baldrige said. "By getting a toehold in the market now, they will have future success."

But Baldrige also lists plusses from the high dollar, which has kept inflation low and forced American companies to get more competitive faster. He said that some companies have reduced costs by 25 to 30 percent but, "in a lot of cases, it's just keeping even with the dollar.

"When the dollar recedes, it will leave them in good competitive shape," he added. " But that's doing it the hard way."