Malcolm E. O'Hagan, The executive director of the U.S. Metric Board, drove to the Washington Monument grounds one sunny morning last month with two members of his staff and three frogs.

While photographers recorded the scene, the frogs jumped and O'Hagan cheered them on-all in the cause of converting the United States from its traditional measures of inches, pounds, and pints to the meters, grams, and liters of the metric system.

"Kilo Monster," the frog who jumped the farthest here, will be shipped to California in mid-May, a spokesman for the Metric Board said, to take part in the annual frog jumpping contest at the Calaveras County Fair.

For the first time in 51 years, he said, the results of the Calaveras frog jump will be reported in centimeters as well as inches.

"The Metri Board called us up," said Raymond Callahan, the manager of the Calaveras Fair, "and asked us to use centimeters, too. We didn't have any objections. So we said we'll do it."

Getting other American institutions to adopt metric measures has not been so easy.

During the past two years there have been some important landmarks on the march to the metric system. Radio stations and bank clocks have started reporting temperatures in Celsius degrees as well as the familiar Fahrenheit. Domestic wine producers have replaced quart bottles with liters. Automobile manufacturers have brought out new models with metric dimensions.

But in the face of public opposition there have also been serious set-backs:

The Federal Highway Administration scuttled a plan to switch all the nation's speed limit signs from miles per hour to kilometers.

The National Weather Service withdrew indefinitely its plan to give forecasts and measurements in metric units.

The Department of Agriculture dropped a proposal to label all fish and poultry products in metrics.

Even though Congress passed a "metric conversion act" in late 1975, which established the Metric Board, it is still a debatable question whether the act made it government policy to encourage metric use.

The General Accounting Office, the Congressional watchdog agency, last October issued a long report, declaring that "national policy is not to prefer one system (of measurement) over the other." The report said any switch to metric system would be costly and have only a slight effect on foreign trade, even though all other major countries now use metric measures.

The report said the Metric Board should remain neutral and only help private groups that want to go metric, anyway.

The board's chairman Louis K. Polk, a retired vice-president of the Bendix Corporation, said the board should not be so "passive."

"We have no mandatory powers," Polk said, 'but we do have a mandate to plan for a voluntary conversion to a predominantly metric society . . . Why would we have a law if we weren't supposed to do anything at all?" CAPTION: Illustration, no caption, By Alice Kresse-The Washington Post