GENEVA (AP) _ Japanese automakers are engaged in ''wrong and wishful thinking'' if they expect stable auto sales in recession-wracked Europe this year, the head of General Motors Europe said Tuesday.

Louis R. Hughes said he expects the total western European car market to fall 8 percent, or 1.1 million units, this year. That would bring total western European car sales to 12.3 million units this year, down from 13.5 million in 1992.

''The boom years are over, 1993 is going to be a tough year in the European car industry,'' said Hughes, who at 43 became the top official for GM of Europe last November. Hughes spoke at a news conference at the Geneva Auto Show.

He said GM expects total car sales to fall 19 percent in Germany and 10 percent in Italy, though there is hope for slight improvement in Britain, where a 3-year recession appears to have ended.

Much of GM Europe's revenue comes from its sales of Opel and Vauxhall brands.

Opel and Vauxhall sold 1.61 million cars in 1992, the eighth consecutive record year.

GM Europe earned $1.23 billion in 1992 with total sales of 1.69 million vehicles, good for 12.6 percent of the European market. That was doen 30 percent from $1.76 billion in 1991. It was also too little to offset $4.5 billion in GM operating losses in North America.

Hughes said that with European economies slumping this year, GM Europe expects further declining profits. He predicted ''reasonable profits'' this year but wouldn't elaborate.

GM was the second-largest European car manufacturer behind Volkswagen AG of Germany, Hughes said.

He said GM Europe could gain market share this year despite lower industry sales.

Hughes unveiled the new Opel Corsa, the latest entry to the small car category, which currently accounts for more than 30 percent of European car sales.

The new Corsa features improved door reinforcements, a roomier trunk, improved fuel efficiency and anti-pollution catalytic converters, said Peter Hannenberger, director of Opel's technical development center.