Brussels — On election night, as the votes were being counted, Olivier Deleuze was blowing a mean sax at a jazz club called Le Gaspi (French slang for ''waste''). The next morning, he woke up to find he had been elected to the Belgian Parliament.
It marked a milestone in European politics - the first time a candidate from an environmental, or ''green,'' party had been elected to a national legislature in Europe, and it confirmed that as a political force Europe's greens are growing.
Long-haired and mustached, Deleuze was one of four green candidates to win seats in the 212-member Chamber of Representatives in Belgium's general elections on Nov. 8. Four more greens were chosen for the 106-seat Senate, and in the voting for both assemblies, the greens took nearly 5 percent of the vote. In the last general elections three years ago, they collected less than 1 percent.
''In voting for us,'' says green bigwig Jean-Marie Pierlot, ''young people especially - but not only - have shown that they are seeking a real alternative. What the established left has to offer is no longer credible.''
Political analysts have been quick to attribute a large measure of the greens' stunning electoral success in Belgium to the newly enfranchized youth vote. Of the 7 million voters, about 500,000 were 18-to-21-year-olds who cast their ballots for the first time.
But beyond numbers, the victory of the Belgian greens, who recorded the largest percentage gain over the 1978 elections of any of the 24 parties, reflects a flowering of environmental consciousness throughout Europe and, more fundamentally, a growing disenchantment with traditional party rhetoric.
As political beings, Europe's greens have grown particularly fertile in France, West Germany, Italy, the Netherlands, and Belgium.
In France, the greens were strong enough to field a presidential candidate in last April's elections. Brice Lalond won nearly 4 percent of the vote and finished a very respectable fifth. In the 1974 elections, the green presidential candidate garnered 1.3 percent, and in the 1978 legislative elections, the greens scored only 2.1 percent.
The situation is different in the Netherlands. Preferring to remain outside politics, strictly speaking, the Dutch environmental movement has developed close and influential ties with existing parties, and some environmentalists have become permanent consultative fixtures in the legislative process. Consequently, environmental legislation in the Netherlands is among the toughest in Europe. Even in the government, the movement's interests are well-represented. Environmentalists call the new secretary of state for the environment, a former parliamentarian, ''one of us.''
The West German environmental party Die Grune (the Greens) may be the most promising alternative political force in Europe. It has already won major victories - and seats - in several state parliamentary elections.
''The environmentalists,'' journalist Werner Birkenmaier wrote recently in the Stuttgarter Zeitung, ''are more than just a passing political phenomenon. Their voter potential is likely to grow, and chances are that they will move into other state legislatures and even the Bundestag (the national parliament). . . .''
In Italy, no green so far has made it as far as the national assembly. But ''it won't be long,'' one analyst says. Meanwhile, 18 radical party parliamentarians represent the interests of Italy's blossoming environmental movement in the assembly.
''No,'' concedes newly elected Belgian green, Olivier Deleuze, laying down his sax between sets, ''I wouldn't say that the gains of European environmentalists in the political arena prove that the traditional system is on the verge of collapse. After all, Belgium's three largest parties, for instance, still took 80 percent of the vote in the recent elections. But I would say that we are now being taken seriously as a political reality, and not just as a bunch of back-to-nature freaks.''