With remarkable ease, the House yesterday approved a three-year reauthorization of the Endangered Species Act--two years longer than Interior Secretary James G. Watt had wanted.

The House approved the bill by voice vote after less than 10 minutes of discussion. It sent it to the Senate, where a similar plan has attracted wide support.

The House measure basically would leave the act intact, but make some changes to improve its administration. The law protects "endangered" and "threatened" plant and animal species.

The bill would speed up the process by which species are added to or deleted from the government's lists. The decision to list a species would be made solely on a biological basis and could not be delayed longer than a year unless there is disagreement in the scientific community.

The act has been opposed by developers, because projects could be delayed if they would threaten a species on the government's list. The act was used to halt construction of the $120 million Tellico Dam in Tennessee for several years because the project threatened the tiny snail darter. Congress later allowed the project to proceed.

Rep. Walter B. Jones (D-N.C.), chairman of the House Merchant Marine and Fisheries Committee, said the bill authorizes funding for the program at existing levels--about $39 million per year. Jones said the bill makes the act "a more effective and efficient tool for the protection of wildlife."

Last year, Watt had asked Congress to extend the act for only one year, saying he wanted time to find administrative solutions to problems that industry has had with the act.

At the behest of the President's Task Force on Regulatory Relief, the department identified 27 sections of the law where changes might be in order. Among them was a suggestion that, because of budget cuts, attention should be focused on protecting birds and mammals rather than lower forms of life.

An agency spokesman said yesterday that the department has been waiting for Congress to complete action on the legislation before moving forward on the regulations. Since the Reagan administration took office, four species have been added to the endangered list--an orchid, two species of desert pupfish and the Hays Spring amphipod, which lives only in a spring in Washington's National Zoo.