The Pentagon's heads-up lettuce policy -- to wrap or not to wrap?

First, it must be stressed that the United States is not - repeat not - developing lettuce-based weaponry.

No MX lettuce (placed in grocery stores, to fool the Russians). No Stealth lettuce (for dieting soldiers. They can eat it only if they can find it). No lettuce sales to Taiwan (will China approve?).

But the role of lettuce in our nation's defense has been the subject of recent debate between Congress and the Department of Defense.

Last week, in a move that appeared unlikely to affect US salad deployment capability, the Pentagon agreed to purchase supplies of unwrapped lettuce for use in Northeastern military bases.

Made under congressional pressure, this decision to relax stringent vegetable procurement rules will help farmers from southern New Jersey make up sales lost earlier this year, when the Department of Defense stopped buying American lettuce for shipment overseas.

''We've convinced the Department of Defense (DoD) that unwrapped lettuce is just as good as wrapped,'' says an aide to Rep. Bill Hughes (D) of New Jersey, a key figure in the fight. ''The congressman does not want American troops to eat bad greens.''

Asked if the decision marks a crucial change in US defense posture, a Pentagon spokesman replied: ''No.''

For more than 20 years, New Jersey lettuce farmers - concentrated in Cumberland County, near the state's southern tip - have sold 15 to 20 percent of their crop to the Pentagon for shipment to US military bases in Europe. Last year, the state sent 1.8 million pounds of greens to US armed forces overseas. But it takes three weeks to ship lettuce from Cumberland County to US military commissaries in West Germany, Spain, and other European countries. By then, says a military spokesman, the greens are a bit brown around the edges.

''It's already in bad shape when it gets there,'' says James McKenna of the Defense Personnel Support Center. ''It's a morale problem.''

Accordingly, the Pentagon has exported seeds and farming know-how in an attempt to coax European farmers into growing the iceberg lettuce favored in American salads. After several years of false starts and bad harvests, the European lettuce industry is finally off and blooming. So last May, DoD informed the lettuce growers of south Jersey that their crop was no longer needed - a move the Pentagon estimates will save $600,000 a year.

''We were really amazed,'' says Erwin Sheppard, a third-generation Jersey lettuce farmer. ''A concentrated effort on their part created competition for us.''

Gloom, like a horde of rabbits, descended on Cumberland County - an area already suffering from 17.7 percent unemployment. Mr. Sheppard plowed under 15 acres of his crop, worth $30,000 retail.

Enter Representative Hughes, the local congressman. After a series of meetings between Hughes, Pentagon representatives, and local officials, DoD in June agreed to purchase 750,000 pounds of Jersey lettuce for use in mess halls. In addition, Cumberland County farmers would be allowed to compete for contracts on the 1.3 million pounds of lettuce sold to Northeast US military commissaries, said the Pentagon - but only if each head of lettuce was individually wrapped.

Lettuce sold in the supermarket-like commissaries must be swathed in plastic, according to military regulations. ''It's consumer preference,'' says James McKenna of the Defense Personnel Support Center.

But the dozen major Cumberland County lettuce growers, none of whose farms are bigger than a few hundred acres, have no lettuce-wrapping equipment. Their small size precludes purchasing the machines, which cost upwards of $60,000.

South Jersey is also wetter than such lettuce-wrapping strongholds as California. Damp heads spoil underneath their plastic overcoat. The machines, which must move about the field, get bogged down in Jersey mud, says John Murz, an aide in Hughes's Cumberland County office.

Hughes went back to DoD. When the situation was explained to them, Pentagon officials agreed that south Jersey farmers could compete for the commissary lettuce contracts, without having to wrap their heads (of lettuce).

But the dispensation is only good through this year's growing season, which ends in late fall. If the farmers of Cumberland County wish to continue as defense contractors, they must develop lettuce-wrapping capability by 1983. Their window of vulnerability, so to speak, is rapidly approaching.

Even with DoD's concessions, figures lettuce farmer Sheppard, his sales to the military will be slashed by a third this year. This winter, he will sit down with fellow growers and figure whether it's economically feasible to form a co-op for lettuce-wrapper purchase.