Albion Plateau, France — The verdant, rolling farmland here in southern France is picturesque and tranquil. But beneath the greenery lie 18 hardened steel and concrete silos, each containing one strategic nuclear missile with enough firepower to obliterate a major city.
These missiles, along with five nuclear-powered submarines and 34 Mirage bombers, make up the world's third most potent nuclear arsenal, France's so-called force de frappe.
In an effort to demonstrate the continuing credibility and independence of the force, journalists were recently given a rare firsthand tour of the missile sites.
The tour came at a moment when the force de frappe is playing an increasingly central part in the argument over the East-West balance of power. Francois Mitterrand's Socialist government recently approved a five-year, $110 billion defense plan with the priority of modernizing France's nuclear force.
French nuclear capacity seems to worry the Soviets. With increasing vehemence , Moscow is insisting that the French force be included in Geneva arms reduction talks.
Although France remains outside the NATO military command structure, it closely cooperates with the alliance and is a strong supporter of the allied plan to deploy new American nuclear weapons. As a result, the Soviets argue that the French force is, in effect, part of the larger allied force.
But Paris resists this view. ''France has an autonomous nuclear force designed only for the protection of France,'' government spokesman Max Gallo said last week. ''Integrating the French forces would tie the hands of French independence. And that France will never accept.''
After he withdrew France from NATO's integrated command structure in 1966, Charles de Gaulle developed the country's nuclear potential as the key to its independent military stature. French defense officials continue to insist that the force de frappe is designed to defend French national territory and France's ''vital interests.'' The French president, they say, and only the French president, can order an attack.
''Right now, it is the SS-20s that threaten us,'' one French Defense Ministry official says. ''But if the US threatened us, we would point the missiles at Washington.''
This boast, however, is not quite true. France could possibly send submarines and jets close to the US coast, but the missiles here at Albion only have a 1, 860-mile range, says Col. Gilles Jonglez de Ligne, deputy commander of the missile base. That is enough to hit Moscow and all major targets in the western Soviet Union, but falls far short of Washington.
Such deficiencies have always raised questions about the effectiveness of the force de frappe. But the Socialists are moving to erase any doubts by investing heavily in nuclear weapons mod-ernization.
While overall military spending will increase by 10 percent in absolute terms this year, spending on nuclear arms will rise by almost 20 percent. The five-year defense plan approved by the National Assembly last month continues this buildup.
A sixth nuclear submarine is scheduled to be put into service by 1985, and another by the end of the decade. Instead of single-warhead M-20 missiles, the subs will be armed with new M-4 missiles, each with a range of more than 2,400 miles and six warheads.
A new Mirage airplane and new, longer-range tactical nuclear missiles capable of hitting Warsaw Pact troops in Eastern Europe are also scheduled to be deployed. Finally, the French have announced that they have developed a neutron bomb, but have not yet decided whether to proceed with development.
Despite this upgrading of its tactical weapons and its flirtation with neutron bombs, France continues to reject the idea of a rational, winnable nuclear war. Its nuclear strategy remains based on dissuading any aggressor with the threat of a massive strike against its civil population.
In the event of an attack, the Mirages would head directly toward their targets. The subs would fire all their 16 missiles. And here at the Albion Plateau, Colonel Jonglez de Ligne says all 18 missiles would be launched within seven minutes of the go-ahead.
''We want to dissuade any aggressor from attacking us by making the cost of that attack too high,'' says Dominique David, a military analyst at the French Institute of War.
Can the force de frappe actually do this? Some military experts argue that despite modernization, French guidance systems will continue to be inferior to US and Soviet versions. There are also worries that a concentrated blast of enemy warheads could knock out all the missiles on the Albion Plateau.
But the overriding consensus of military analysts seems to be that the French nuclear deterrent is credible.
''Sure, the French guidance systems may not be quite as accurate as the American system,'' a US analyst based in Paris says. ''When you are aiming for cities though, it doesn't matter if you are 100 yards or three miles from the actual target. The French can get their missiles to the city, and destroy the city.''
The land-based missiles are vulnerable, the analysts say, but even if they are destroyed, the more mobile submarines and Mirages will remain.
''It would be impossible to get all the submarines,'' David says. ''And in a half hour, the submarines alone could kill 50 million people. That should be enough to dissuade any adversary.''
This threat makes the force de frappe the wild card in any scenario of European war.
By insisting that the French weapons be included in the Geneva talks, Moscow takes this view. The Soviet concern could merely be a negotiating position worked out for propaganda purposes, but privately US officials here admit that the French nuclear arms are a key ingredient in the alliance's defenses.
''By having an independent nuclear force, the French contribute to the defense of the West,'' the American analyst says. ''The Soviets always have to consider that the French would retaliate by themselves. And, after all, the French are on our side.''