OTTAWA (AP) _ Led by the first monthly increase in industrial production this year, Canada's economy grew by 0.4 percent in April, the government's Statistics Canada said Wednesday.

Gross domestic product, which measures the value of all goods and services produced by Canadians, increased to an annual level of $128.7 billion (Canadian) in April from $128.2 billion in March and $123.1 billion a year earlier. The figures are in inflation-adjusted 1971 dollars and have been adjusted for seasonal variations.

The increase in gross domestic product in April followed gains of 0.5 percent in March and 0.1 percent in each of the previous two months.

Meanwhile, the increase in industrial production, which accounts for about a third of total economic output, was a strong 0.8 percent and followed declines of 0.2 percent in March, 0.4 percent in February and 0.8 percent in January.

The resumption of production in April following labor disputes in the brewing industry in Ontario and rubber and plastics industry in Quebec accounted for almost 85 percent of the growth in manufacturing.

Meanwhile, lower interest rates are believed responsible for the first substantial rise in construction activity in 12 months as both residential and non-residential building activity increased in April.

In the services industries, the strongest increases were in the finance, insurance and real estate industries.

The major losers in April were motor vehicle parts manufacturers, pulp and paper mills, sawmills and producers of office and store machinery. Exports of wooodpulp, newsprint and office machinery fell during the month.

In the services sector, there was a major decline in wholesale trade following a significant 5.9 percent surge in March. There was also a slight decline in retail trade following a large jump in March.

Widespread declines in retail trade were partially offset by a sharp increase to record levels in sales by new car dealers.