Old Land Rovers never die here. Their aluminum shells are cut and pounded into cooking utensils, and their springs are hammered by blacksmiths into ax heads. The rest is cannibalized to keep other Land Rovers going.

The corn crop in the Lomba River valley stretches 20 miles to the horizon. It reminds you of Iowa.

And the screaming industrial lathes in the jungle workshops at Jamba and Likua sound like Detroit.

The crops will feed the rebel army and the large civilian population in this remote bush country, and the open-air workshops seem, to a visitor, to be building enough motorized weaponry to transform Jonas Savimbi's guerrilla force into a relatively powerful conventional army.

This has become a land of ingenuity where Savimbi's National Union for the Total Independence of Angola (UNITA) has created a state within a state, a thriving mini-economy within a battered national one.

There is no currency. The system is GI: Everything is government issue, from food, clothing and tools to the "luxury" items, such as cigarettes and soft drinks, that come in from South Africa and are dispensed from grass warehouses run by a central administration.

Liquor is not available. In fact, it is prohibited. Savimbi says the people can drink when the war is over.

Thus, Savimbi's UNITA functions not only as a political and military front, but also as the central government for half a million people who live in the "liberated territory" he controls.

UNITA's total revenues have never been disclosed. Savimbi claims that he receives assistance not only from South Africa, but also Morocco, Burkina Faso, Senegal, Saudi Arabia, France and the United States. In an interview, Savimbi said he is also receiving "some few millions" of dollars from the sale of diamonds taken from captured mines, and from trading Angolan teak to a South African lumber firm. Other estimates put the total in the tens of millions of dollars. UNITA Aims for Self-Sufficiency

But beyond this direct aid and outside barter, UNITA since 1980 has established an industrial and agricultural base that takes advantage of the natural resources and war booty available in the region.

In the Jamba garment factory, soldiers learn to sew on 46 old Singers that the plant's manager said are turning out 10,000 uniforms a month from bulk cotton cloth purchased outside the country.

Savimbi's Jamba headquarters, which did not exist before 1980, has grown into a hidden city of 12,000 guerrilla and civilian residents. A policeman in white gloves directs traffic at the main crossroads.

Here and at Likua (pop. 8,000) six hours up the road, people live in modest grass huts. But rebel engineers have built power plants out of captured diesel generators and have strung wires through the forest to light hundreds of these grass-roofed homes.

Diesel fuel and gasoline are among the commodities essential to keep Savimbi's mini-state operating, and during a heavy month of consumption his camps and fleet of 700 trucks may burn nearly 100,000 gallons, according to the logistics officer here.

Road graders can be seen putting a hard pack over the soft, sandy path to the Jamba airstrip, where too many heavy trucks have buried their axles in the deep ruts.

Health care is distributed from more than 20 small hospitals, according to Dr. Henrique Raimundo, UNITA's health secretary and a Lisbon-trained physician, and dozens of open-air classrooms operate year-round for the children.

Col. Ernesto Mulato, a civil engineer before the war, is in charge of the expanding agricultural projects UNITA has undertaken to feed its population. But the thick, fine sand underlying most of this bush land forced Mulato to look farther north for good soil. He found it just outside Mavinga, where the Lomba River has deposited a thick layer of topsoil drained from the rich earth of central Angola.

After UNITA captured Mavinga in March 1981, it was safe to plant there. Today, the entire valley is shoulder high in bloom.

"We are gradually becoming self-sufficient in our food production," Mulato said.

The most impressive structure UNITA has erected is at Likua. It can only be described as a five-acre, open-air factory where the battlefield hulks of Soviet-made trucks, tanks and armored personnel carriers are being rehabilitated and altered to give Savimbi what his enemy has: motorized striking power.

In charge of Likua and UNITA's military logistics is a onetime guerrilla commander, Altino Sapalala, whose left hand was sheared off by machine-gun fire as he was leading an ambush on a truck convoy in July 1978. He goes by the nom de guerre Brigadier Bok and is among Savimbi's most senior and trusted strategists. 'We Throw Nothing Away'

In Bok's open-air shop, changes are made to machinery and weaponry to improve their performance in the harsh climate and terrain of southern Africa. The weapons and trucks come mostly from the Soviet Union. Others are West German-made.

After a 1985 offensive in which Savimbi's forces drove the Angolan Army back from Mavinga, Bok said UNITA captured the greatest haul of tanks, armored cars, trucks and weapons in the history of the war.

"Every time they attack Mavinga," he said, "we get a lot of equipment." It is all dragged back to Likua and Jamba where, Bok said, "We throw nothing away until it is of absolutely no use to anyone."

And, he added, "Out of every three captured truck engines, we get one good one."

UNITA has learned who makes the best machinery for the kind of abuse it takes here. For instance, Bok said the Soviets make the best heavy truck in the world and the worst gasoline engines of any industrial country.

As a result, Bok's engineers have designed a way to drop the old engines out of Soviet trucks, custom tailor new motor mounts and install a high-quality West German diesel (purchased from South Africa) in its place. The new truck has been dubbed the "Yankee" and its engine, shocks and gear box will hold up longer than any guerrilla transport UNITA has tried, Bok says.

His men are now studying how to remove the weak gasoline engines from a dozen Soviet armored assault vehicles to get them back on the road for UNITA with sturdier power plants.

Transport is all-important here because Savimbi's army and small guerrilla units are strung out along supply lines that stretch several hundred miles north from his southeastern enclave.

To ensure that his trucks can run at night in dangerous areas near the battlefront, Bok said his men have extracted the infrared night-vision scopes from Soviet-made T55 tanks captured last year at Mavinga and installed them in some of UNITA's heavy transports.

Now, he said, UNITA drivers "don't have to use their headlights" for risky deliveries.

About 300 UNITA soldiers work at the Likua factory. A few had mechanical skills in the beginning and they have taught the younger ones. Frayed repair manuals have been gathered into a small library to help the apprentices learn how to tear down engines, do valve jobs and fire up an arc welding machine.

They are using this knowledge to rehabilitate sophisticated Soviet weapons. Among UNITA's booty from last year's offensive are a half-dozen multiple rocket launchers mounted on mobile Soviet trucks. These are the deadly "Stalin's organs" that can lay down, in a matter of seconds, a fearsome barrage of 27 rocket bombs on a target 15 miles distant.

The latest model Stalin's organ has a computer-driven fire control system, according to Fonseca Santos, Bok's engineering chief in Jamba, where the weapons are under repair. In recent months, Santos said, UNITA has mastered the system and will deploy the rocket launchers, equipped with captured rockets, in time for the expected 1986 offensive.

The rebels call all that they have built since 1980 their "infrastructure," and if the war ends, some of the people are talking about staying here. Others will take skills they have learned here back to the towns.

But the future is still too murky for most to think about. After all, when the war is over, said one young officer, "We may be dead."