General Motors of Canada Ltd. says it will spend $2 billion over four years on new plant operations that will create more than 3,300 jobs in the Ontario cities of Windsor and St. Catharines.

F. Alan Smith, the president of GM's Canadian subsidiary, said Thursday about $1.5 billion will go toward a new front-wheel drive automatic transmission plant at Windsor, which will double production and triple its work force to 3,800 from 1,200.

The second-largest project, conversion of the engine plant to build V-6 engines and a new transmission casting plant at St. Catharines, will mean an additional 700 jobs.

NUCLEAR CONTRACT: Westinghouse Electric corp. has signed a $267 million contract to supply Korea Electric Co. with two nuclear reactors and two turbine generators for planned nuclear power plants.

Westinghouse won the contract, signed in Seoul Thursday, after intense internation bidding involving a dozen American, West German, French, British and Japanese companies.

LAYOFFS: Olivetti and Co. said it will lay off 4,500 workers in 1981 in a reorganization being made by Carlo De Benedetti, the new managing director of Italy's largest computer and office machines group.

Unions called strikes in all Olivetti factories next Wednesday and 15 hours of stoppages in the next 10 days.

JAPANESE IMPORTS: Japan's September licensed imports totaled $9.89 billion, up 32.5 percent from a year earlier, but down 14.3 percent from the previous month, the Ministry of Internal Trade and Industry said yesterday. p

Measured in yen, imports licensed in the month totaled 2.138 trillion yen, up 51.1 percent from a year ago, but down 14.6 percent from the prior month.

The measure, licensed imports, differs from the balance-of-payments method of calculating foreign trade, but the report is viewed as an indicator of trends in Japanese international trade.

Imports of fuel, including crude oil, reached $6.571 billion, up 58.7 percent from September 1978.