Britain's newly elected Conservative government unveiled its legislative agenda today, pledging stringent curbs on the authority of trade unions and municipal governments that have long provided powerful support for the opposition Labor Party.

In the traditional state opening of Parliament, Queen Elizabeth II read an address prepared by Prime Minister Margaret Thatcher. With its overwhelming majority in the new House of Commons, the government is assured of getting most, if not all, of its program adopted.

The speech reaffirmed the Tories' intention to continue selling nationalized industries and maintain an economic strategy designed to keep inflation low while beginning to tackle the country's high unemployment. These measures are a continuation of Thatcher's first-term policies, and she said today that no radical departures should be expected in the years ahead.

The queen's speech reflected Thatcher's increased determination to reduce the sway of unions and eliminate the metropolitan councils, which are controlled by Labor.

These are moves ostensibly to increase members' influence on union leadership and to save public funds by abolishing a layer of government. Nonetheless, they would deal another major blow to Labor's national influence.

The measures were denounced by union spokesmen. Miners' leader Arthur Scargill threatened that "extraparliamentary action" would be taken if the legislation is adopted--meaning strikes and other protests. However, the results of this month's national elections and recent votes in many unions, including the miners, indicate there is considerable public backing for reforms along Thatcher's lines.

For the most part, the legislation unveiled today had been tipped in advance. Plans for selling such major enterprises as British Telecom, the country's telecommunications company, were under way when Thatcher dissolved Parliament in May and called an election.

On foreign policy, the speech underscored Conservative support for Reagan administration nuclear arms proposals and pledged to go ahead with plans to buy U.S.-made, submarine-launched Trident missiles.