Ever since the beginning of the 1970s, the 4-day work week has seemed to be just around the corner, but this time it looks for real, one reason being that in a hit-and-miss way the country is already within striking distance of it.

The movement away from the long-entrenched 5-day, 40-hour week is being spurred by a combination of forces, including chronic unemployment, the need to spread work around, the fast-growing market for part-time employees, and the desire of an ever larger number of Americans for more leisure time.

All this is culminating in an organized drive against the 40-hour standard. Last week the All Unions Committee to Shorten the Work Week was launched in Detroit, while in Washington various friendly committees in the House and Senate were considering new bills looking toward the same end.

The 700 union leaders who attended the Detroit meeting agreed that the fastest way to cut unemlpoyment is to cut the work week - without, of course, cutting pay. "That wind is there," says Frank Runnels, a founder of the union committee. "It's blowing up into a storm."

Douglas Fraser, president of the United Auto Workers, sees a shorter week as "absolutely inevitable." The only question in his mind is "how fast we get there." Fact is, the UAW is almost there already.

The contracts it signed in 1976 with the Big Three automakers and the leading producers of farm equipment gave nearly a million workers a total of 12 extra days off with pay this year and next. Added to holiday and vacation time, this gave UAW members over 40 paid days off each year.

If that subsidized leisure were applied on a regular day-a-week timetable, the union would even now be within hailing distance of its goal of a 4-day, 32-hour week at the same pay it gets for a 5-day, 40-hour schedule.

At present, there are roughly a million Americans already employed on a 4-day basis, but they are nearly all working 10 hours a day, which has not aroused much enthusiasm since it means longer hours without overtime pay.

The only surprising thing about the organized drive for a shorter week is that it didn't come sooner, for the 40-hour week has been the established norm for 40 years, or since Congress passed the Fair Labor Standards Act of 1938. Before that, the work week had been whittled down time and again.

Back in 1791, Philadelphia carpenters struck for a 10-hour day. The average employee then put in 12 hours a day, six days a week, for a total of 72 hours. By 1860, the work week declined to 68 hours, gradually dropping to about 50 hours in the 1920s.

Then in rapid order came the Great Depression, the advent of the New Deal and collective bargaining, and finally the historic 1938 labor act which established the present 5-day, 40-hour week by requiring employers to pay time and a half for all work in excess of 40 hours.

Rep. John Conyers Jr. (D-Mich.) has introduced a bill that would cut the standard work week back to 37.5 hours and then to 35 hours by mandating overtime pay for longer hours.

At the dept of the Great Depression, incidentally, the Senate overwhelmingly passed a 5-day, 30-hour law, but the House killed it. Also, President Carter, during the energy shortage last year, urged adoption of the 4-day week as a means of saving fuel, but there has been no White House follow up since the crisis eased.

The very first president of the American Federation of Labor, Samuel Gompers, said, "as long as we have one person seeking work who cannot find it, the hours of work are too long."

The Gompers dictum is still being echoed by such labor leaders as Edward Fitzgerald, head of the United Electrical Workers, who says "the unemployment lines will grow and grow in this country until we get the shorter work week."

Since 1947, the weekly average of hours worked by non-farm employees has already fallen from 40.3 to 36.1, a drop of 10.4 percent. The reasons are more women in the work force, higher productivity, the growth of service industries and, above all, the big increase of the permanent part-time wrok force, which now numbers over 16 million people, most of whom do not want to work full time.

The part-time trend is likely to continue, for both Congress and the Carter administration are taking a benign interest in it. One study shows a million jobs would be created if merely 20 percent of the work force put in three hours less a week, or 20 days less a year.

Another study shows that many part-time workers are more productive than full-time ones. Also a committee headed by Sen. Gaylord Nelson (D-Wis:) heard testimony that more part-time jobs might reduce heart-attack deaths, family breakups and, among other things, relieve traffic congestion. Wow.