House and Senate panels voted yesterday to extend the embattled Endangered Species Act for three years, rebuffing Interior Secretary James G. Watt's campaign to have it extended for only one year.

The measures would also force Watt to speed up the addition of species to the list, a process virtually stalled since he took office.

The House Merchant Marine and Fisheries Committee voted unanimously to extend the 1973 act, best known for holding up the $120 million Tellico Dam in Tennessee as a threat to the tiny snail darter. A subcommittee of the Senate Environment and Public Works Committee sent a similar measure to the full committee, which is to vote on it next Tuesday.

"This is an issue that people care about deeply. It is an issue that goes beyond narrow special interests," said Sen. John H. Chafee (R-R.I.), chairman of the Senate panel and sponsor of its bill. ". . . We are seeking to preserve the diversity of life and slow the accelerating rate of species loss."

The 1973 act is designed to protect rare flowers and animals, particularly when threatened by development projects. Industry and federal agencies must obtain exemptions from Interior's Fish and Wildlife Service to proceed with projects that threaten the survival of 222 American animals and 61 plants on the endangered list.

The act has been heatedly opposed by industries ranging from utilities to furriers to mining companies. It is just as fervently defended by conservation groups who point to increasing extinction rates among plants and animals, comparing the process to "burning books before you've read them."

The amendments added by both the House and Senate panels are designed to speed both the addition of species to the endangered list and the process of granting exemptions to industry. Industry lobbyists yesterday called the provisions workable, and conservation groups voiced qualified praise--a consensus few expected during months of stormy debate.

Both the House and Senate bills are aimed at reversing Watt's policy of considering the economic costs of adding a species to the list instead of weighing only biological evidence. Watt defends his policy by referring to President Reagan's executive order requiring cost-benefit analysis of all new federal regulations.

Both bills say Interior must consider "solely" biological criteria in adding a species to the endangered list. A committee staffer said the House panel will "flush its report profusely with language explaining this meaning so it is not misinterpreted."

Conservation groups charge that Watt used the Reagan executive order to frustrate the intent of the act. Some 60 proposed new listings were bottled in the Interior solicitor's office last month awaiting cost-benefit clearance, long after they had passed the biological test. Only one species cleared the rigorous cost-benefit test--a tiny crustacean known as the Hays spring amphipod, which lives only in a spring in the heart of Washington's National Zoo and whose listing apparently threatens no development projects.