All new nuclear power plants would be allowed to go into full operation before the completion of safety hearings under an industry-backed bill that passed the House Energy and Commerce Committee yesterday.

Supporters easily defeated 10 Democrat-sponsored amendments aimed at weakening the licensing speedup proposal, which allows the Nuclear Regulatory Commission to order unlimited full-power operation as soon as each finished plant passes NRC staff safety tests, whether public hearings are finished or not.

The nuclear industry pushed the bill as a money saver, arguing that prolonged public hearings will force 15 plants scheduled to be completed over the next two years to sit idle for as long as a year each, costing consumers more than $2 billion.

The measure, attached to the NRC's fiscal 1982-83 budget authorization of $500.7 million, passed on a voice vote. A similar but weaker version has passed the Senate Energy and Natural Resources Committee, and backers are confident of winning final legislation this session.

Democrats attacked the bill for going too far, even beyond the Senate committee version that would permit new plants to operate only at 5 percent of full power before hearings finish. The full-power authorization is "excessive and dangerous," said Rep. Edward J. Markey (D-Mass.). "This would be voting to unlearn the lessons of Three Mile Island."

Rep. Toby Moffett (D-Conn.) said the blaming licensing delays on public hearings was a bogus argument, since most of the plants are involved in "important and serious" safety issues that need discussion. Markey argued that the true causes of licensing delay are labor, financial and construction problems.

Reps. Carlos J. Moorhead (R-Calif.) and Tom Corcoran (R-Ill.) responded that the NRC retains discretion under the bill to issue a lower-power license instead of a full-power one and to withdraw the operating license altogether if hearings reveal some reason to do so.

The House Rules Committee last month killed another speedup proposal. It would have spurred nuclear power plant licensing by restricting public access to hearings and requiring formal, legalistic affidavits to precede the offering of evidence on safety matters.