The Senate yesterday shelved an effort to help rescue the financially troubled Washington Public Power Supply System in the Pacific Northwest as it moved toward a showdown on the controversial coal-leasing practices of Interior Secretary James G. Watt.

Faced with filibuster threats, proponents of a rescue plan for the default-plagued electrical power system, known as "Whoops" after its abbreviation, WPPSS, agreed to lay the plan aside temporarily so that action could proceed on a $7.6 billion Interior Department appropriations bill.

The bill had been held up for two months by Sen. Howard M. Metzenbaum (D-Ohio), who charged that a WPPSS rider championed by Sen. James A. McClure (R-Idaho), chairman of the Appropriations subcommittee with jurisdiction over the bill, amounted to an indirect federal bail-out that could cost the U.S. Treasury as much as $1 billion.

McClure denied the charge, saying that the proposal simply would expedite financing to complete two power plants not involved in a recent WPPSS bond default and that he would pursue the plan.

Still pending before the Interior bill can be passed is a proposal by Sen. Dale Bumpers (D-Ark.) and other Democrats to prohibit coal-leasing until a special commission reviews Watt's leasing practices and Congress can decide whether to allow resumption of leasing.

The House has approved such a moratorium, while the Senate rejected it, 51 to 48.

The House yesterday gutted more than one-third of a $10.8 billion spending bill for the federal judiciary system and the Commerce, Justice and State departments, and sent the leftovers to the Senate, 228 to 142.