Brussels — A year ago today, the Soviets touched off 365 days of superpower brinkmanship that disarmament campaigners and others would like to forget, but never will. The Geneva talks on limiting nuclear weapons in Europe fell silent when the Soviet negotiator walked out Nov. 23. The race by the United States and the Soviet Union to deploy new nuclear missiles in Europe began within days.
This week, NATO officials confirmed that 102 new US nuclear missiles have been deployed in Britain, West Germany, and Italy since last December under a NATO plan to station 572 intermediate-range missiles in five Western European countries by the end of 1988.
Also this week, a senior US State Department official, noting that the Soviet SS-20 construction program has ''continued vigorously'' in the past year, confirmed here that the number of medium-range SS-20s aimed at Europe and elsewhere is certainly higher than the 378 announced by NATO last December - although the exact number varies from day to day because of an ambitious base reconversion program begun several months ago.
Perhaps even more disquieting, according to NATO officials, are recent Western intelligence reports that the Soviets have begun building more than 10 new missile bases in the past 12 months - the largest number of such bases started in any one year since the SS-20 was first deployed in 1977.
''This leads us to the inevitable conclusion that the number of SS-20s deployed by the Soviets will increase significantly over time,'' the State Department official said.
Western officials emphasize that, in contrast to the Soviet program, the NATO plan approved in 1979 calls for ''modernizing'' the nuclear arsenal in Western Europe and not increasing it. At least five nuclear weapons will be withdrawn from NATO's nuclear stockpile for each cruise or Pershing II missile deployed under the NATO plan, the officials point out.
''When these reductions are completed,'' according to Assistant Secretary of State James Dobbins, ''NATO will have reduced its nuclear arsenal by approximately one-third, to its lowest level in more than 20 years.''
This ''numbers game,'' however, has done little to silence critics of US and Soviet policy.
In Brussels earlier this week Msgr. Bruce Kent, head of Britain's Campaign for Nuclear Disarmament, said that ''we have all reached grotesque levels of overkill.''
''Like drunken men standing in a cellar full of petrol, we quarrel over who has the most matches,'' he added.
Like it or not, however, the superpower row over ''matches'' remains central to avoiding what Msgr. Kent calls ''a nuclear war which no one can win.''
Last June, for example, the Dutch government decided that it would deploy its share of the 572 new NATO missiles (48 cruises) only if the number of SS-20s deployed by the Soviet Union had increased beyond 378 by Nov. 1, 1985.
Thus, assertions by the US that Moscow has boosted deployment of SS-20s in recent months have brought indignant reactions - not surprisingly - from the Soviet Union, which says that it has done no such thing, but also from the Dutch , who claim that the US has provided no proof.
US officials have said the number of SS-20s deployed fluctuates from day to day, making precise counting impossible. Some Western officials, in fact, have said that on any given day the number may be lower than 378.
This in part is due to the Soviet program, revealed by NATO this week, to reconvert some SS-20 bases, apparently to accommodate new SS-25 intercontinental nuclear missiles.
Some NATO officials concede the Soviets may in fact not be increasing the the number of SS-20s in ''deployment status'' as a ploy to dissuade the Dutch from stationing new US cruise missiles on their territory under the NATO plan.
Whatever the Soviet motive, the threat to the alliance, particularly to the US, will increase significantly through the deployment of the new, longer-range SS-25 intercontinental ballistic missiles, NATO experts agree.
Figuring too in the ''matches'' game is tiny Belgium, which so far has failed to give the go-ahead to its share of the new NATO missiles (48 cruises) - although construction at the site set aside for the weapons, south of Brussels, has begun.
Belgian Prime Minister Wilfried Martens said this week that the government's decision would depend on the ''international situation,'' an apparent reference to the possible re-opening of the Geneva arms talks.
''Before taking a decision, however,'' Mr. Martens said, ''we will want to evaluate relations and negotiations between the Americans and the Soviets.''