In ordinary times, Wallace Wilson would plant his 30 acres of tobacco and be done with it. He would plant some market vegetables and tend to his beef, but the tobacco would pay his bills and assure his security.

But these aren't ordinary times for tobacco farmers in the great southeastern leaf belt, and Wallace Wilson is girding for the day when his tobacco security blanket is jerked away.

Since colonial days, tobacco has been the lifeblood of this region -- the biggest cash crop, the crop that built an economy. Tobacco is still king, but the federal price-support program that underpins the farmer has come on hard times and growers are hunkering down for big changes.

Unlike major crop farmers in other areas, who can't or won't change farming patterns even though their economic fortunes look bleak, Wilson and others around here are looking for new ways to help tide them over the tough times they think are coming.

And one secret of survival, they hope, may well be . . . broccoli.

By turning to vegetables and specialty crops, tobacco farmers in states such as Virginia and North Carolina, with their proximity to the populous Boston-Richmond corridor, believe they have the potential to outcompete distant California, Texas and Florida in terms of price, transportation cost and freshness of product.

In an odd way, the American farmer has become a victim of his own success. He has abandoned the diversity and hard work that made his farm nearly self-sustaining, producing its own food and replenishing its soil through rotations and natural fertilizers. The new rigidity is easier, but the farmer who grows only wheat has little to fall back on when his markets erode.

As it is in wheat country, so it is in the Tobacco Belt. Overproduction, falling exports and high operating costs have got many farmers who rely on tobacco in serious trouble.

Those who are diversified may survive; the rest may be too late.

Adding to their troubles, Wilson said recently, is the allotment system -- government growing permits -- in the federal tobacco-support program. "We can't make it with the leases we have to pay for the allotments owned and rented out by nonfarmers . We can't make it if the markets remain stagnant and if consumption continues going down.

"But we're in an ideal spot here for vegetables. If we manage our broccoli program right, if we get the facilities we need for handling our crops, this could turn out okay. We're not giving up tobacco. We're just trying to be ready if more problems turn up."

Wilson's friend, Bobby Conner, president of the Southside Virginia Produce Cooperative, put it this way:

"We're fearful we might lose some of the tobacco program, so we need other cash crops. We don't want to seem like an ostrich with our head in the sand. Some skeptics say that if we spent all this energy on tobacco, the program would be saved. But in the long run, if we can weather the problems, we may be better off with broccoli and other crops."

The U.S. Department of Agriculture, by most accounts, does little with its vast scientific and agronomic network to wean the economically stressed farmers away from their reliance on a few grain crops and back to the varied farming styles of their forebears. Help, if it comes, is through the state-run extension services.

The Virginians have had a little help from the USDA, but their case is an exception. Looking for Alternatives

Virginia's tobacco farmers are ahead of tobacco farmers in the rest of the region in searching for alternative crops.

Spurred by advisers from Virginia Tech, Wilson and 104 tobacco farmers in 10 counties have formed a cooperative and set about to find new fortune in broccoli and cantaloupes.

Their broccoli, grown for the fall market, last year went to supermarkets as far north as Washington.

Plans are moving ahead to build a $500,000 cold storage and icing plant that will let farmers expand their plantings this year to 1,000 acres from last fall's 207.

Their analyses show the plant will pay for itself if the fall broccoli market is as big as they think it is. And the building will allow expansion to other market crops.

The broccoli project was the brainchild of Larry McPeters, the Halifax County extension agent who may have seen tobacco's dark future before most people here. He started the wheels of change rolling.

"This year [1984] tobacco will be a $38 million crop in Halifax, but there have been a lot of complaints about the program. We identified a lot of problems with tobacco -- profit margins were smaller all the time -- and agricultural leaders around here agreed we had to look at other crops. I set up a 28-man task force to look at what else we could do."

After long meetings and after crop specialists from the USDA and Virginia Tech studied the possibilities, the Virginians decided to try their hand at broccoli. McPeters in 1982 planted test plots to show that the crop could do well in the fall.

In 1983, their cooperative by then organized, the farmers planted and harvested about 28 acres. This past season, they harvested 207 acres of broccoli in 10 counties and found that they could have sold more, at higher prices, if they had had the supply and a way to keep their crop longer in cold storage. Expanding the Markets

The increased acreage means there is more work for local farm laborers, and the work at the co-op means there are jobs for local young men. As co-op manager David Slabach talked about the last of the fall harvest, a steady stream of young men came into the building to ask about work, to ask about more hours or to pick up paychecks.

"The most important thing to the co-op now," Slabach said, "is finding a way to finance a storage and icing facility that will allow us to expand our plantings and to expand our markets. The facility will determine whether we make it . . . . You can see already, from the traffic of these fellows coming in, that we can provide an important additional source of employment if we can expand next year."

"What pleases me is that we have a quality broccoli pack and we have created demand. The buyers now call us . . . they like the broccoli and they want to know what else we have available. It's really frustrating to see these opportunities and have to let them go by because we're not yet ready do do more," he said.

Farther north, in the Burkeville-Appomattox area, Virginia Tech extension specialists have mounted another program to get tobacco growers to think about diversifying. Agricultural classes were started in Nottoway County last fall and will continue this year. The state is also setting up a demonstration farm near Burkeville to test vegetable varieties and show farmers how they can make the move away from tobacco.

"Ten years ago, farmers weren't ready for this," said Wayne Compton, the extension chief in Appomattox. "We're trying all we can think of to get them to look at diversifying . . . . We already know that some of the supermarket chains are eager to get fresh products from this area. We have a tremendous advantage -- we can pick a crop this morning and have it at the store in the afternoon." North Carolina Efforts

Similar things are going on next door in North Carolina, the major flue-cured tobacco state. Extension agents at North Carolina State University and North Carolina A&T State University are urging farmers to look at alternatives to tobacco as a cushion if the federal program is changed drastically.

Extension economist Ed Estes, directing an N.C. State tobacco-alternatives program, said, "We're trying to identify the areas where we have some advantage because of climate and location in making more inroads into the vegetable market. We're trying to show farmers not to just fold up the tent."

"We are trying," Estes said, "to replace some of the income that is going to be eliminated if the tobacco program dies . . . . The dominant feeling here is that there won't be a program, the profits will be eaten out of it. A vast majority of these tobacco farmers will go out of business -- the most hurt will occur among the little and small-to-medium operations."

Not everyone, of course, can grow broccoli. Estes said that he and his colleagues are looking at approaches that will let farmers plant a number of vegetables for harvest over a longer period. "We are looking at crops where overall demand is up -- broccoli and cauliflower, fresh tomatoes, peppers, cucumbers," he said.

North Carolina A&T, a predominantly black school, is playing a variation on the same theme.

"Our work here is not just because of the tobacco situation," said Dr. Daniel Lyons, small-farm program coordinator. "Our farm opportunity program, with about 700 farmers participating in a 20-county area, is geared to the small and part-time farmer and horticultural crops they can produce for a decent income with little extra expenditure."

A&T's program includes a network of agricultural "paraprofessionals" assigned to work with farmers on every kind of problem that might come up, from planting to taxes and financial planning. "If the farmer has a problem, he knows who to call," Lyons said. Easing into the Future

No one pretends that the shifts in farming structure that could result from changes in the tobacco program can be cushioned entirely by growing other crops. But calls for preparing farmers to deal with the squeeze, when and if it comes, are being heard increasingly along Tobacco Road.

A recent report from the Rural Advancement Fund/National Sharecroppers Fund warned that the tobacco program is in mounting trouble and urged policy makers to help ease farmers into other crops. The study proposed an earmarking of some revenue from the federal tobacco tax to a fund to help farmers diversify.

Legislation introduced last year in the North Carolina General Assembly proposed creation of a committee to help ease farmers through the transition. A state Council of Churches tobacco study panel called for more research on "alternatives to tobacco in the economy of the state."

Here in Halifax and surrounding Virginia counties, they're beyond that stage. "Land is no problem here," said county agent McPeters, "and we must encourage farming. I think this vegetable thing can go, but we need help. My only interest is in seeing these farmers make a living."