Brussels — Overshadowed but not overlooked - that best describes the French and British nuclear arsenal. Independent of NATO weapons, the mostly sea-based French and British versions of the nuclear deterrent are the subject of intense discussion at home and at the superpower negotiating table on European limited-range missiles.
The 64 missiles aboard Polaris submarines have become the center of a raging controversy in the British election campaign because of the opposition Labour Party's stand that they be scrapped. Meanwhile, the French Socialist government has encountered virtually no opposition to its recent proposal that another missile-carrying submarine be added to its ''force de frappe.''
Both have steadfastly rejected Mocow's insistence that it be allowed to maintain 162 of its current 350-plus SS-20 missiles aimed at Western Europe to counter this Franco-British arsenal. London and Paris consider their weapons as being entirely national and strategic and therefore having no relevance to bilateral United States-Soviet negotiations devoted exclusively to tactical missiles.
NATO strategists have also always maintained that the French and British arms are strictly up to those countries and not for discussion by the superpowers in Geneva. They are viewed by governments in London, Paris, and the other NATO capitals as a national deterence against nuclear annihilation or blackmail by the Soviet Union, even if American nuclear protection were somehow nullified.
''They can't hit a barn,'' notes one European expert about the French and British nuclear weapons, ''but they are good weapons of last resort. They are a signal to the Kremlin that if Britain and France were attacked, enough of their missiles would get through to wipe out Moscow, Leningrad, and probably some other cities. They are credible to that extent.''
A number of Europeans also wistfully regard the Franco-British forces as a possible base for a truly independent European defense and nuclear guarantee.
Britain and France have 64 and 80 submarine-based missiles, respectively. The British Polaris missiles have three warheads each, but all three land in a cluster on the same target. Somewhere between one-third and one-half of these 144 sea-based missiles are operational at any one time.
France also posesses 18 land-based missiles on the Plateau d'Albion in the Vaucluse region of southern France. But like the superpowers, France is aware how vulnerable land-based deterrents are, and opted to expand its submarine force in the most recent budget presented a few weeks ago.
Prime Minister Margaret Thatcher has also committed the British government to modernizing its submarine nuclear deterent with the acquisition of the Trident system from the US. This would mean that in the latter part of the decade, the French and British nuclear arsenals would increase by some 1,100 warheads.
But in Britain, the opposition Labour Party has come out strongly against these plans and in favor of scrapping the British nuclear force. Labour's stance , however, has aroused considerable public fears, and some of the more moderate Labour leaders have recently sought to distance themselves from this position.
While Britain and France also have several hundred other nuclear missiles and aircraft considered tactical by them and the Soviet Union, Moscow has repeatedly tried to include the longer-range European arms in nuclear negotiations.
Although the US and Western European allies rebuffed these previous Soviet attempts to pull British and French nuclear weapons into past strategic-arms talks, they were seen as the reason the Soviet Union was allowed to retain more nuclear arms than the US in the strategic arms limitations talks (SALT 1) treaty of 1972. A protocol to the unratified SALT 2 pact also looked ahead to negotiations about European-based nuclear systems.
And while French official and public opinion remains adamant that their arsenals not be included in negotiations, there is widespread feeling in Britain and other NATO countries that there might be circumstances under which these forces would be the subject of negotiations.
British Foreign Secretary Francis Pym repeated this distant possibility again last week. But Defense Minister Michael Heseltine and other British officials were quick to emphasize that this could only be ''following a major and quite different, changed level of deployment by the superpowers.''
They also underlined it did not imply a change in British policy and should not be seen as a signal to the Soviet Union that Britain is prepared to discuss the Polaris-Trident force.
Some experts do foresee that the British and French arsenals might be involved in either the Intermediate Nuclear Force (INF) talks or the strategic-arms negotiations in Geneva, or perhaps another broader forum, such as the proposed European conference on disarmament. They expect that the Soviet negotiators might again be willing to drop their demand in the INF talks, but that the prospects of later discussions on Franco-British forces be held out as an inducement for Moscow concessions.
London's prestigious Economist magazine suggested the number of French and British missiles be spread between the intermediate and strategic talks, and possibly allowing the Soviets to keep a few more SS-20 and other strategic missiles than the US, to counterbalance the West European arms.
France, however, seems irrevocably attached to its independent force. ''The French are a rogue elephant,'' notes one analyst, ''and no French government could survive if it took its finger off the nuclear trigger. The British Trident might be up for grabs, but that's not likely as long as France keeps its force.''