In the aptured German Foreign Office files of the U.S. National Archives is a letter sent in November 1940 by Soviet Foreign Minister Vyacheslav Molotov to Nazi Foreign Minsiter Joachim von Ribbentrop. It says, in part, "The territorial ambitions of the Soviet Union lie south of Soviet territory in the direction of the Persian Gulf."

In August 1941, in concert with Britain, the Soviet invaded Iran, seizing Azerbaijan, Iran's chief northwestern province. In 1945, at the end of World War II, two Soviet-backed governments were set up there. They were not crushed by the shah's armies until December 1946, six months after President Truman forced the Soviet occupation troops to withdraw.

On Dec. 11, 1976, the annual celebration of Azerbaijan's liberation took place 15 miles outside of Tehran, on the road to Karej.

Down the road to the left, out of sight, massed squares of troops were drawn up. Across the vast plain, clean and empty in the weak winter sun, rose folded, red-brown mountains, slightly whitened at their tops by fresh snow.

The spectator stands were filling solid. Tea was served hot and eagerly taken by everyone. A few spectators sat trying to get warm in front of cheap kerosene heaters. Some were uniformed, their overcoats ablaze with medals.

After a wait we saw a covered care coming, a Mercedes. A woman's figure learned forward from the back seat, waving: the empress.

Then one's eye was caught by a movement down to the right, far down the road. A small caravans was starting. In front was a single bay horse. The clatter of hoofs came to us, ckipped and clear. Behind the single wearing silver breastplates and helmets, tricolor pennants fluttering from the tips of their lances.

The leader sat his horse well, and as he drew abreast, a rippling took place in the crowd as it rose to its feet, hands clapping, but with a certain restraint, tolerant but not kind. On came the figure, the shah on the horse, clad in a khaki uniform with jodphurs, his hand barely touching the outsized peak of his military cap.

Around me people rose applauded politely. They were, it turned out, a reliable, handpicked crowd: secret police officials, old generals, senators, senior bureaucrats. The mounted shah passed from sight. For a minute there silence, then, in the distance, rose a vast, steady male cheering as he came within sight of his troops.

The army is everywhere in Iran, but no one speaks of it. In very town one comes across a train of parked khaki trucks along a curb, men in green fatigues lounging about a headquarters doorway. If you drive over the Elborz Mountains you suddenly pass a barbed-wire enclosures, grim and featureless, where uniformed men with bayoneted M-16s turn and look at you coldly as you pass.

It was Reza Shah, the shah's father, says the scholar Amin Bahani, "who instinctively undestood the lesson of European history - that the emergence of unified national state coincides with the development of a national standing army." Under Reza Shah, the army became the chief representative of the new elite and the new order. Marvin Zonis, a scholar on Iran, wrote: "The loathing of many Iranians to the House of Pahlavi is chiefly based on their loathing of the army.

Under Reza Shah, the army was raised to social heights that surpassed those of many of the old families. After the 90,000-man army was defeated in three days when Britain and Russia invaded in 1941, feelings against the Rahlavi dynasty ran high. A Cabinet minister told me that when the present shah took power, he had to be taken through the streets secretly, to avoid mobs of demonstrators.

Today, Iran's army is the largest in the Persian Gulf region, numbering more than 300,000 plus 81,000 in the air force and 18,500 in the navy. Military conscription is for 25-years - two years of active military service and 23 years of reserve.

In the name of the Nixon Doctrine, which requires regional powers to conduct their own defense, Washington set Iran up as a kind of super gendarme for the area.

When Middle East oil-exporters, led by the shah, raised their prices in 1973, Iran seized the chance the new wealth offered to begin a military buildup that dwarfed anything in the region. By the time it has finished its weapons-purchasing program, Iran will have more British-made Chieftan tanks than the British, more American-built Phantom F-4 fighter-bombers than Israel, plus 80 F-14s, the most advanced tactical jets in the U.S. Navy's inventory, and the largest troop-carrying Hovercraft fleet in the world.

Iran's importance to the United States consists of three-factors: its anticommunism, its oil and its strategic localtion. All three factors are closely tied to Anglo-American oil interests in the Middle East.

At the end of World War II, the coal-powered industry of war-wrecked Europe was in the hands of Communist-controlled labor unions. To counter this and what he regarded as the spread of "international communism," President Truman sent $400 million in military aid to Turkey and Greece and sped the U.S. 6th fleet to the Mediterran. In Tehran, the U.S. Army Mission Headquarters (ARMISH) was established in 1947.

Meanwhile, labor troubles in the coalfields plagued the Continent, and the American oil companies raced to develop their Middle East oil reserves to market in Western Europe.

When the anti-Western Premier Mohammed Mossadegh fell in 1953 and the shah was returned to the throne by the CIA, the chief benefit to the West was that the route by which American-owned Middle Eastern oil made-its way to Western Europe and been secuver.

"Iran is the windpipe," a veteran business consultant of Iran said recently. Iran controls the northern shore of the Straits of Hormuz, through which oil must pass. Some 80 per cent of Japan's oil supply, 75 per cent of Israel's, 85 per cent of Australia's and 40 per cent of U.S. oil requirements filled from abroad pass through the straits.

The security of the straits is a manor Iranian defense aim. The most serious fear is that one day they could be mined and American are flying mine-sweeping missions in the Persian Gulf.

In Shiraz, I interviewed a Sikor-sky pilot from Olympia, Wash., who said he was flying such missions in the big 212 helicopter. He showed me both his company and his Iranian army ID.

An official at the State Department who deals with Iranian affairs denies that such missions are military but admitted that they would become so "the first time a mine is found."

"You cannot imagine the bitter humiliation of having a national life where you can only do what another, a foreign will, allows you to do; where you are never free from their scrutiny, their medding, their contempty."

The speaker was an Iranian educator, and I have heard his passionate loathing of Russia echoed in many Iranian voices - in men like Ambassador Ardeshir Zahedi a d Gen. Hassan Parkravan, a former head of SAVAK, Iran's secret police.

The Soviet Union to the north, with its 1,250 mile-long common border, and Iraq, Russia's ally, to the northwest, are Iran's two biggest defense worries. Three times in this century the Russian bear has slouched south and badly mauled the Iranian lion.

The impotent chagrin at having seen their country conquered, occupied, partitioned is a deep grievance for Iranians. But the Iranian military establishment has purposes that go beyond any probably impossible dreams of major resistance to a Soviet attack.

American critics of arms for the shah often ignore the armed forces' importance for the stability of his regime; the critics do not, however, ignore the fact that the armed forces give Iran major leverage over its less-armed neighbors - Iraq, Pakistan, Afghanistan, Saudi Arabia and all the Arab emirates of the Persian Gulf.

For Iranians, their new Westernized army satisfies considerations of prestige as well as of strategy and tactics. It symbolizes their breath-taking rise to power. The huge military acquisitions keep morale and loyalty high not only in the army itself, but among the country's elite generally.

One day in the mountains, the deep valleys covered by a fresh, sugar-white snow, I walked with an Iranian official. Dark clumps of bare trees marked distant farms. The winter country was peaceful and quiet, not a soul in sight and the only sound the cawing of a single crow. "This, this is the land we refuse to give to the Russians," said the prominent Iranian.

For him and many others, Iran's new military might is a symbol of how far they have come from the past.