The United States reversed course in its policy toward Chile yesterday, voting in favor of a$55 million development loan from the World Bank after several months of abstaining on other loan requests to protest Chilean human-rights violations.

State Department officials said that the move was in response to President Augusto Pinochet's ending of Chile's state of siege. But a key member of Congress protested that the change was premature and was made without required notification to Congress.

"I can't accept this immediate change in our position and violating the law with regard to consultation as a reasonable response to the Chilean government just making this announcement," said Rep. Stan Lundine (D-N.Y.), chairman of the House Banking, Finance and Urban Affairs subcommittee on international development institutions and finance.

On Monday, Pinochet lifted the state of siege and press censorship that had silenced his opposition since Nov. 6. He cited "an appreciable drop in the systematic subversion that had required the imposition of the state of siege."

A milder "state of emergency," involving curfews and limited censorship, remains in effect.

The Reagan administration has abstained on votes involving loans to Chile by any multilateral bank since early February. Lundine said State Department officials briefed the subcommittee several times since then on the Chilean situation, but mentioned no planned change in policy.

Lundine said that the subcommittee had "picked up a hint" from sources outside the administration that a policy change might come Thursday, when the World Bank is to vote on two other development loans to Chile.

Lundine and Banking Committee Chairman Fernand J. St Germain (D-R.I.) wrote Treasury Secretary James A. Baker III yesterday before the vote, reiterating that they expected to be consulted first. Lundine said that neither had expected a vote so soon.