A federal judge, ruling on an increasingly controversial issue, yesterday barred the Labor Department from enforcing a new minimum wage for foreign migrant workers coming to Virginia to help harvest the tobacco crop.

The order, issued in U.S. District Court in Roanoke by Judge James C. Turk, was a victory for the Danville-based Tobacco Growers Association which has angrily opposed the federally set $3.51 hourly wage standard.

Turk did not specify with the wage rate for alliens should be. the growers have suggested $3.20.

The court ruling was the latest development in a series of disputes in Virginia and elsewhere stemming from the hiring of foreign migrant workers by American agricultural producers.

The Labor Department recently set off widespread protests by proposing to set the hourly minimum wage for alien migrant workers by a new nationwide standard, instead of the current state-by-state method. Under this proposal, the minimum wage for foreign farm workers would rise to $4.51 an hour -- $1 higher than the Virginia standard rejected to Judge Turk.

In Virginia, there also have been disputes in recent years centering on Labor Department efforts to require apple growers to employ Puerto Rican rather than Jamaican, migrant workers.

John S. Edward, the United States attorney in Roanoke, said the government would seek an expedited appeal of Turk's order by the 4th U.S. Circuit Court of Appeals in Richmond.

At issue in yesterday's ruling were efforts by southside Virginia tobacco growers to hire about 1,100 Mexican migrant workers to help harvest the tobacco crop between August and early October.

The growers contended they could not find enough American field hands to harvest their crops, but they asserted that the recently set $3.51 hourly wage minimum for alien farm workers was to high.

In contrast, American farm workers currently must be paid a minimum wage of $3.10 an hour -- the amount the Virginia tobacco growers describe as the prevailing pay rate for their workers.

The government argued that the $3.51 minimum, which was set for all alien migrant farm workers hired in Virginia, was a reasonable standard. It was computed, according to Edwards, by applying the average 18.7 percent increase last year in Virginia agricultural workers' wages to the 1979 standard for foreign migrants. The minimum wage for alien migrant farm workers hired in Virginia last year was $2.96.

The minimum pay standard, known as the "adverse effect" wage rate, is intended to protect American farm workers from unfair competition from alien migrants. The movement contended that the same method for computing the wage minimum has been used for 12 years, unheld by other courts and found valid in Labor Department studies.

Turk rejected these arguments, saying that the $3.51 wage minimum set for alien migrants in Virginia was "not reasonably related" to the aims of protecting American tobacco workers from foreign competition. He confined his ruling, however, to the tobacco business and did not order the Labor Department to change its method of computing the minimum pay rate for other alien agricultural workers.