Vice President Mondale, warning that the independent truckers' strike is jeopardizing the economy "at a moment when we can least afford it," yesterday urged the truckers to return to the nation's highways. He said the roads are "open and safe."

Speaking on behalf of President Carter, who is in Japan, Mondale said that the adminstration has adequately addressed the concerns of striking truckers this week by ensuring equal distribution of diesel fuel and raising the fuel recovery surcharge from 6 to 7 percent.

"A fast end to the strike is now crucial," he said. "In South Carolina, in Texas, in Florida, in California and other states, there are crops that must be moved. Action by some truckers is putting jobs in jeopardy and threatening food shortages and the economy in general."

Mondale's warning was seconded by Agriculture Secretary Bob Bergland, who said at a separate news conference that if the truckers' strike continues much longer, delays in delivery of perishable farm products will have a measurable impact on consumer prices.

The administration's plea that the truckers return to the highways was quickly rejected by the leaders of the various trucking groups involved in the 20-day protest.

"What they say is of little or no significance," said Doug Biddle, a representative of the 30,000-member Independent Truckers Association. "Every night when we look in the mirror, we tell ourselves that we should return to work. We know we're losing money, but we can't go back until all our requests are met."

John Mohay, president of the National Independent Meat Packers Association, added, "We need more than just a request. We need protection for the drivers who want to work, to eliminate and minimize the fear of violence. The truckers also need additional revenue and adequate fuel."

Although leaders of the independent truckers' movement yesterday maintained that their strike was gaining momentum, there were indications in certain regions of the country that more truckers were, in fact, returning to the highways.

In Virginia and Maryland, for example, major diesel fuel depots that only last weekend were doing little or no business reported yesterday that business was back to 75 percent of normal.

Officials at the Interstate Commerce Commission, which has been attempting to monitor the strike, said several states in the South and Southwest also seemed to be handling more truck traffic yesterday then they had in several days.

According to federal officials, the impact of the strike was being felt most profoundly in the food industry. Major meatpackers were operating on a day-to-day basis according to the availability of trucks.

One major supplier, B.C. Dressed Beef of Omaha, recalled its 400 workers yesterday after a two-day layoff, but others reported continued layoffs.

Major grocery retailers in the Washington area say the direct impact of the strike has been slight. Wholesalers, however, say the slowdown and higher fuel prices are boosting shipping costs and adding a few cents to the cost of vegetables and fruits.

In Virginia, Gov. John Dalton said his state police will provide escort protection for trucks hauling the $40 million potato, string bean and cucumber crops from the Eastern Shore farms, where growers are concerned that their vegetables will soon rot if not moved to market.Maryland Gov. Harry Hughes issued a similar directive yesterday.

According to several federal officials, the dozens of independent trucking leaders who have come to Washington this week to make their case seemed most interested in a lifting of the truck-weights limits in several states that have regulations more restrictive than the 80,000-pound federal standard.

According to the ICC, four of the 12 states with the restrictive truck-weights laws - Iowa, Missouri, Mississippi and Connecticut - this week have imposed emergency measures to raise them to the federal standard. In Maryland, one of the states that has yet to raise the truck-weight maximum, Hughes is scheduled to meet with state independent trucking leaders this morning.