Six years after Congress set up a board to direct the country's voluntary conversion to the metric system, the world of meters and kilograms is still a long way away, and the government is doing relatively little to bring it any closer.

For scientists and large international industries in high-technology fields, this makes life difficult. Large businesses are faced with a sort of language barrier, operating in a country that uses the inch-pound system, while trading with a world in which the metric system is almost universal.

For small businesses, for labor unions who worry about foreign imports and their impact on jobs and for large segments of the American public, this is no problem. Their position: let's convert to the metric system on an industry-by-industry basis, and only when there's an economic need.

At the center of these political crosscurrents is the U.S. Metric Board, an agency that metric supporters once thought would promote the virtues of the metric system, but which reversed its role a year ago and became an advocate of the go-slow approach.

The board, a 17-member commission with representatives of large and small businesses, labor unions, consumers, educators and scientists, was created when Congress passed the 1975 Metric Conversion Act.

Like the act, the board's mandate was something of a compromise: it had no regulatory authority over private industry or government agencies. Congress had decided not to choose between the metric system and the customary system of weights and measures so the board's job was simply to coordinate conversion efforts, to be a liaison between government and industry and to educate the public.

At first, the board, and many government agencies, were enthusiastic for the brave new metric world. But the public's reaction to the first federal conversion efforts did a lot to dampen spirits. Proposals for metric highway signs, metric fish and poultry labeling, and for gradually replacing Fahrenheit temperature readings with Celsius measurements in National Weather Service reports met with sharp disapproval. The agencies involved retreated in disarray.

After that experience, "various federal agencies said, 'I don't want to be the first one out here,' " said Roger Travis, a small business man from Massachusetts who sits on the Metric Board. "Nobody wanted to be first."

That included the Metric Board.

In the three years that it has operated, the board has served as a liaison between industry and government and an information clearinghouse; it has commissioned 14 studies, at a cost of $700,000, on the status of metric conversion in various industries, the problems associated with conversion and its virtues.

During those years, the members who tend to support the metric system have gradually been eclipsed by labor, small business and consumer representatives who usually agree that the metric system is more logical than the customary one of feet, gallons and pounds, but who think economic considerations, not pure mathematical logic should be the driving force behind conversion.

The balance of power shifted decisively during a board meeting last year when, after much argument, the board passed a resolution saying its mission was to "accommodate" metric conversion--not "facilitate " it.

"Unless there's an economic gain to be derived I don't think there will be conversion," said Travis. "Those industries that want to convert have converted--mostly large multinational organizations."

According to the American National Metric Council, a private trade group, most pharmaceutical and photographic products are marketed with metric measurements, wine is sold in metric bottles and many grocery products are labeled both ways. About 18 percent of gasoline stations now sell by the liter. Perhaps most importantly, General Motors, which has tens of thousands of suppliers, plans to be completely metric by 1983.

"There's no need for McDonald's and Dunkin' Donuts to change," Travis added. "This country will be on a dual system forever."

The Metric Board probably won't last that long. The Reagan administration has proposed eliminating the agency next Sept. 30. The Senate Approprations Committee agreed; the House did not. The issue should be resolved in conference.

Meanwhile, government agencies are approaching the subject gingerly. The official policy is for agencies to "encourage and support an environment which can accommodate metrication." Within that framework there is divergence, with most agencies lacing their policies for conversion with a host of qualifiers like "compatible with the capabilities of industry."

The Defense Department has gone further than most other agencies; it plans to list all its purchase specifications under both systems by 1990.

The go-slow forces feel government agencies will not always be so shy about pushing for metric conversion, particularly if the metric board is not around to look over their shoulder. "The board takes metric out of the bowels of bureaucracy and makes it visible," said Tom Hannigan, a board member and member of the International Brotherhood of Electrical Workers. "With us gone there won't be any focus on it."

This, metric supporters feel, may be just as well.