Britain's government has approved plans for a third major airport for London by 1990, Press Association, the British domestic news agency, has reported.

The agency said the government has approved plans to expand the regional airport at Stansted, 30 miles north of London, and will announce the decision in June.

Supporters have been trying for 20 years to get another airport to ease congestion at London's Heathrow, west of the capital, and Gatwick, to the south.

The decision by the ruling Conservative Party comes after a 38-week study conducted last year, and is strongly opposed by the opposition Labor Party, environmental and residents' groups.

The Labor Party argues that instead of enlarging Stansted, the airport at Manchester, the major north England industrial city, should be expanded to create jobs in that economically depressed region. Labor says the expansion of Manchester Airport also would make the north more attractive for high technology industries.

The government plan calls for expanding Stansted to handle 15 million passengers a year by 1990. The airport currently handles 527,000 passengers a year.

In addition, a fifth terminal would be built at Heathrow by 1990, to boost its capacity from 38 million passengers a year to 53 million. Heathrow handles more international passengers than any other airport in the world.