The U.S. Labor Department has proposed an average 50 percent increase in the minimum wage for alien farm workers, provoking heated protests from farmers in Virginia and elsewhere who legally bring in thousands of such workers each year to harvest apples, tobacco, and other crops.

The increase -- from about $3 to $4.51 an hour -- is needed, Labor Department officials say, to discourage farmers from hiring foreigners who are willing to work for less than Americans and tend to drive down the wages of American farm workers.

The farmers charge that not enough American workers are available to fill seasonal harvesting jobs.

If the major wage hike goes into effect, they say, it will fan inflation, cause serious economic losses for farmers, and may lead to the hiring of more illegal aliens as farm laborers.

"This is a killer," said S. Steven Karalekas, a Washington attorney who represents tobacco farmers in southern Virginia, and apple and peach growers around Winchester, Va., nearby Maryland, and eight other states.

Karalekas charged that the proposed wage increase is "an undisquised attempt to kill the (alien worker) program." The program has been authorized for several decades by U.S. immigration laws to fill jobs for which not enough willing and able U.S. citizens can be found.

Labor Department officials have been trying to cut back the program for several years.

In 1977, apple growers in Winchester obtained a federal court order forcing Labor Secretary Ray Marshall to permit the entry of the alien workers.

In 1978, the Labor Department spent about $300,000 to fly in about 1,000 Puerto Ricans, who are U.S. citizens, to pick the apple corp. But farmers complained that few of them could do the work, and most quickly went home.

Last year the Puerto Rican government refused to let its citizens sign up for the seasonal farm jobs, which last only four to six weeks.

Apple farmers in Virginia and Maryland were allowed to bring in about 1,700 workers from Jamaica, which has been sending workers here for decades. About 750 workers from Mexico came to harvest tobacco in southern Virginia.

Overall, about 18,300 foreign workers received Labor Department permission last year to harvest crops in the United States. Most came from the West Indies and Mexico.

"Last year we kept everything very quiet," said Judy Sorum, a special assistant to Labor Secretary Marshall. "We wanted to study what was happening. This year we decided that some minor regulatory changes were needed."

Although harvest workers generally are paid piece-rate wages, based on the amount of a crop they pick, farmers must pay at least a legal minimum. For Americans, this was $2.90 last year and now has risen to $3.10 an hour.

For aliens, the minimum is set by the Labor Department. Traditionally, it has varied from state to state, depending on local pay levels, though always at least a few cents above the U.S. minimum wage to prevent an "adverse effect" on American workers. Last year, for example, the minimum for alien farm workers was $2.96 in Virginia and $3.06 in New York.

Under the proposed Labor Department regulation, Sorum said, the new minimum wage for aliens would be uniform across the country. It would be set at the expected hourly average for all U.S. piece-rate farm workers, and would also apply to Americans working on farms where aliens are employed.

"If we allow employers to pay (aliens) below the average amount for U.S. workers," she explained, "then we can't ensure that there would be no adverse effect [on U.S. workers]." She added that the higher rate would provide a fair test of whether U.S. workers are available to do the harvest jobs.

Karalekas rejoined that making the expected average wage for Americans the minimum permitted the aliens "would dramatically inflate all wage costs to employers."

The number of American farm workers already is decreasing rapidly, he said, partly because of welfare and unemployment compensation programs as well as federal efforts to train migrant laborers for steady nonfarm jobs.

Most of the shortage has been made up by illegal aliens, he said, who are far more numerous than legal foreign workers brought in with Labor Department permission.

"Farmers would rather not be using illegals," said C. H. Fields, assistant director for national affairs of the American Farm Bureau. "But this new (minimum wage) is going to drive farmers to use more illegals even if they have to risk having the Immigration Service show up and emptying their fields."

Fields said the farmers have enlisted the support of about 20 congressmen, headed by Reps. Dan Daniels (R-Va.) and Hamilton Fish Jr. (R-N.Y.), in their drive against the higher wage.

Their first effort has been to seek a 60-day postponement in the deadline for comment on the new rule, which is now set for April 10.

Sorum said there is "every possibility" that the Labor Department will extend the comment period until Mid-May. She said the department would consider the comments, but hoped to issue the new rule in time for it to go into effect for the autumn harvest season.