In a war of growing racial bitterness, black nationalist guerrillas are mounting a major campaign to drive white farmers off their land just as planting time approaches. The attacks are growing despite their possible devastating effects on next year's harvest and food supplies.

More than 200 farms already are officially listed as "vacant" and half a dozen farming districts - several of them within 100 miles of Salisbury - are more or less abandoned because of the constant guerrilla threat.

While this is still a small proportion of the 6,600 registered white farms, the number of white farmers sticking it out in war-torn Rhodesia has dropped in the past few years from 6,100 to around 5,800 and is steadily declining.

Guerrillas may well be zeroing in on the rich white farmsteads in preparation for a radical land reform permitting the resettlement of tens of thousands of black peasants now living in the country's poor, overcrowded tribal trust lands.

Rhodesia is one of about a dozen countries in the world producing enough both to feed itself and to export surpluses, thanks to its incredibly productive white farmers settled on the best lands. Until recently, nearly half of the country was reserved for 275,000 whites, leaving 6.7 million blacks to eke out a living on the rest.

There is some indication that control of the land has become linked with the visibly mounting racial bitterness as the war drags on. One of the guerrillas who killed 10 survivors of the air Rhodesia Viscount crash earlier this month was heard to shout, "You (whites) have stolen our land" before opening fire.

One sign of the increasing danger for white farmers is that the army is reportedly suggesting to those living in some particularly "hot" districts that it might be better if they "consolidated" themselves into more easily defendable points. But Prime Minister Ian Smith last week reassured those hanging on in the guerrilla threatened eastern border area that "no farmer will ever be told he's got to go.

"Nonetheless, he too hinted that it might be better for beleaguered farmers in districts like Melsetter, 50 miles south of Umtali, if they regrouped themselves in order to faciliate the over-stretched army's task of defending them.

The problem for white farmers is not that the countryside is becoming swamped with guerrillas but that they are switching tacics.

No longer are the guerrillas only blasting the well-protected white farmsteads with borders and rifle fire in nighttime hit-and-run raids. They have now turned to driving off the farm labor, ordering black workers to return to their tribal trust lands and sometimes burning down their grass-and-pole huts if they refuse.

Since last March, scores of farmers have faced this problem in northern and eastern Rhodesia. Just last week, the local press reported three white farms were burned out in the Shamva district 40 miles northeast of Salisbury. On one, 30 black homes were set afire.

In addition, white farmers living on lonely, dirt sideroads face an increasing threat of ambush by guerrillas. Scores have already been killed in this manner.

Just how much this new guerrilla campaign is going to affect the planting of crops over the coming two months is still not clear, but government authorities and the local white Rhodesian press are clearly worried about it, compounding the general uncertainty among white farmers over their future here.

"Harvest of Fear" the magazine Illustrated Life Rhodesia called the coming season. "Guerrilla sights are focused on the farmers of Rhodesia," it began. "The insurgents are aiming to drive men off the land both by terrorizing them and by making it impossible for growers to plant and reap their crops."

"Econonmy Waiting for Vital Crop Decisions" was the recent frontpage headline of the Rhodesian Financial Gazette. It said that "most farmers are delaying final planting until the last possible moment while they try to assess the likely course of events over the next year."

Yet, according to various farming association sources, many white farmers are more anxious than ever before "to stick it out" because of the expectation that economic sanctions will be lifted once a black majority government takes over next year. This in turn would assure far higher prices for export crops.

The economic sanctions imposed by the United Nations after whites here declared their independence of Britain in November 1963 have required farmers to pay high prices for imports while their goods sold away below the going world rate.

"We are aiming at an expansion of our crop of 10 per cent so to be in a position to deal with a sanctions free market," said Donald Bullock, president of the Rhodesian Tobacco Association in an interview. "Our objective is to regain our position on the world market as a major tobacco growing country."

Bullock said the industry, which has 1,600 growing members" and an international reputation, also hopes to increase the crop by 10 per cent every year thereafter.

Such enthusiasm and ambitious plans are hard to match with the host of uncertainties hovering over the future of white farmers in Rhodesia. Yet Bullock, like Denis Norman, president of the Rhodesian National Farmers Union, remains bullish. Sales of seed and herbicides are higher than last year and fertilizer about the same, according to Norman, who also estimates farmers" planting intentions" to be similar to those of a year ago.

He said 50 per cent of them had already made up their minds to go ahead and plant. But, he added, generally "they want to be in a less vulnerable position" in case they cannot reap the next crops.

As for tobacco growers, who can practically smell the higher prices promised once sanctions are lifted, "unless physically stopped from doing so, they will go ahead," according to Bullock. "If they have not their labor force still, they definitely will. A bloke doesn't give up very easily here," he added.

Tobacco is in many ways a bellweather of the rich Rhodesian farmer world, since its growers also produce half of the country's staple corn corp. "The overall farming picture depends on tobacco," said Bullock.

Most of the tobacco crop is not planted until the end of October just before the rains set in. But the 10 percent of it normally grown in irrigated fields is now reported to be going in on schedule.

Just how this struggle for the land and homesteads between white farmers and the guerrillas will end remains unclear, but it stands more than ever at the heart of the war in Rhodesia today.