Liz Hammond pointed to the massive iron grill used to keep guerrillas from a barn and said, "We barricade ourselves in, similar to how medieval knights lived."

It would be hard to differ with her after a tour of the J. J. Hammond farm, 70 miles north of Salisbury, in this area where the guerrilla war officially began in December 1972.

Actually, the Hammonds count themselves among the lucky, compared with many of the dwindling total of about 5,500 white farmers who play a key role in keeping this embattled, unrecognized nation afloat.

The Hammond farm has been hit only once recently by Patriotic Front guerrillas fighting to overthrow the limited black-majority government of Prime Minister Abel Muzorewa. That attack, in May, involved only the burning of a store. There were no casualties.

Although the vast majority of white farmers are still sticking it out, the nagging question of whether it is worthwhile grows as the war escalates, and the guerrillas concentrate on trying to drive the farmers off the land.

For the government the answer is a matter of life and death. Agriculture is the most important industry. It provides 50 percent of the foreign-exchange earnings and makes Zimbabwe-Rhodesia one of the few African countries to be self-sufficient in foodstuffs, according to Dennis Norman, president of the Rhodesian National Farmers Union.

The Union represents white farmers who produce practically all of the agricultural cornucopia, partly because whites control almost all of the best farm land.

One neighbor, Len Leighton, had four "visits" from the guerrillas during a seven-week period despite progressive escalation of his security system. It now includes electric fences, microphones installed in the African compound for early warning, a nineman "militia" of African farmers given rudimentary training by the military and "Adams grenades" -- grenades planted around the property and wired to detonators inside the farmhouse.

Another neighbor, Anthony McClaughlin, who recently received about $28,000 in compensation from the government for 20 warehouses of tobacco that were burned by the guerrillas, put the matter simply: "I expect to be attacked every night."

Norman is enthusiastic about the future because he says he believes economic sanctions against the country will be lifted within the next October-to-June agricultural season, with great benefit to the farmers.

He said, however, "It is getting tougher to convince farmers to stay." They regard next week's London settlement talks as "the last hand of cards to be dealt," he added.

Since Rhodesia's unilateral declaration of independence from Britain in 1965, the number of white farmers has slipped from 6,300 to the current estimate of 5,500 Norman said.

"The loss of another 1,000 farmers Norman said, adding that the country "would go from being a food exporter to an importer," raising the prospect of some starvation.

The country is still experiencing a net outflow of about 1,000 persons fromt he 250,000 white-majority population. Most of these, however, are young people living in the cities who do not have a significant stake in the country and who also face the prospect of long-term military service.

Leighton described the plight of farmers, saying, "If I leave this country I cannot take my farm with me." Despite complaints about low prices and the security situation, he acknowledged that farming in Zimbabwe-Rhodesia provides a comfortable living for whites. "I can't live this way anywhere else," he said.

Most of theempty farms are in the border areas, particularly near Mozambique, according to Norman, who said these are marginal agricultural areas except for the grazing of cattle.

The heartland of production of basic commodities such as tobacco, maize, cotton and soybeans is within an 80-mile radius of Salisbury. It contains about 2,500 white-owned farms that produce about 80 percent of the country's crops.

Norman said 200 to 250 farms in this area are unoccupied, as the guerrillas intensify their efforts to drive the whites off the farms to cripple the government.

Around Centenary there are no vacant farms, but other areas have been hit harder. In Mtepatepa, 80 miles north of Salisbury, at least 15 of the 60 farms have been abandoned, according to Pat Taff, who experienced his fourth attack in 10 days late last month.

Seven famr workers and dependents were killed in that latest raid, but Taff said he was going to stay and was concerned about getting the workers busy building new huts so they would not flee.

Taff wearily said h had lost count of the number of times his farm had been hit in the seven-year-old war, but he thought it was around 17. The worst, until the current series, was in 1974, when his farmhouse was hit by nine mortar rounds and two rocket-propelled grenades.

In the last 18 months, Taff said, "Things keep getting worrse. It has been cooking up especially" since February, he said.

Most farmers seem to feel they are their own best protection. J. J. Hammond probably is typical. The only time he takes off his pistol is when he goes to bed, and then a semiautomatic rifle is at his bedside.

His wife Liz carries no weapon, although she had undergone training as a police reservist. She worries that the war has polarized people and frets that her five sons, all eager to go for their military service, have become "a bunch of right-wingers."

She ruefully acknowledges how the war has changed life on the farm. "You grow up with the security fencing, you get used to it," she said. "The grenade screens [around the windows] are outdated not because they use rockets."

She apologized for the makeshift china service and seating at lunch. All their good things have been moved to their apartment in Salisbury -- "just in case, you know." Salisbury is called "fairyland" because of its distance from the war.

Her husband, who had just returned from a visit to Australia, was showing visitors around a neighboring farm as dusk descended. Liz anxiously phoned and suggested he get his visitors home immediately, gently scolding, "Have you forgotten how we live in this country?"