James G. Watt, confirmed by the Senate yesterday as Ronald Reagan's interior secretary, will be sitting in judgment on dozens of companies that apparently have underwritten his conservative legal foundation in Denver or have support its litigation efforts.

The roster of contributors to the Mountain States Legal Foundation is a corporate who's who, many of whose fortunes are affected by Department of Interior decisions.

A $50,000 contribution from the Scaife Family Charitable Trusts of Pittsburgh headed a 1978 list of donors to Mountain States. Gulf Oil Corp., a major source of income for the trusts, mines uranium, coal and oil shale on public and Indian lands in the West and has mining-permit changes pending at the Interior Department.

From the Adolph Coors Foundation of Golden, Colo., came $35,000. The foundation derives income from the Adolph Coors Co., a brewing firm whose mining affiliate has coal-stripping plans pending at Interior and which leases oil and gas on public lands in Colorado. Foundation tax files here indicate that Coors gave on additional $25,000 in 1979.

Joseph Coors, a contributor to conservative political causes, heads the company and is a founder and former board chairman of Mountain States.

Spokesmen for the Scaife family trusts and the Coors foundation did not respond to questions.

A Mountain States representative refused last week to comment on the authenticity of a list of supporters of its various courtroom moves, many of which have been aimed against Interior Department regulatory actions in the West.

Income tax data on public file here, however, confirm that Mountain States received contributions from some of the interests having a stake in Interior Department decisions and actions.

Watt was president and chief fund-raiser of the foundation, which describes itself as devoted to fighting "execesive bureaucratic regulation and the stifling economic effects resulting from the actions of extreme environmentalist groups and no-growth advocates."

Watt could not be reached for comment last week, but during his confirmation hearings two weeks ago he declined repeatedly to name contributors to Mountain States. At the same time, however, he promised to "recuse" himself from decisions in which conflicts might arise.

He said that disclosure of his foundation's financial supporters was not required by law and that foundation board policy prhobits employes from making such disclosures.

Led by Sen. Dale Bumpers (D-Ark.), several Democratic senators unsuccessfully pressed Watt for names during the Energy and Natural Resources Committee hearings. The Republican-controlled committee last week recommended Senate confirmation of Watt on a 16-to-0 vote, with Bumpers and Paul Tsongas (D-Mass.) abstaining, and the full Senate approved his nomination yesterday, 83 to 12.

Bumpers' questions were based on information contained in a list of Mountain States contributors made available to the Arkansas senator.

A number of the firms involved in energy and resource development on public lands have business pending at the department. According to outgoing secretary Cecil D. Andrus, firms on the list have at least 47 applications pending for approval of various actions.

Dozens more of the firms supportive of Mountain States litigation already are under Interior regulation. They include Amoco, Cities Service, Chevron USA, Occidental Oil Shale, Marathon Oil and Shell Oil in the energy field; Amax, Consolidation Coal, Kemmerer Coal, Phelps Dodge and others in the mining and minerals business.

At one point during his confirmation hearings, Watt indicated he knew the names of only some contributors to Mountain States. At another point he said he could not say who they are.

But throughout, Watt assured his interrogators that he would be impartial in running the department and that he would remove himself if necessary from decisions that might involve conflicts iwth contributions to the foundation.

Under current procedures, Watt apparently would be the sole judge of potential conflicts. The Senate committee does not have Mountain States' contributions lists, the data are not available to the public through the Internal Revenue Service, and a foundation representative said last week that the foundation's "hard and fast" policy is to disclose no names. l

"The lists are confidential. Our donors are big people and little people. We consider their contributions a private matter. If they want to tell you, it's up to them," she said.

Mountain States' contributors, largely from the West, include oil and gas firms, mining firms, utilities, construction companies, developers, banks, transportation and media groups -- most of which have a stake in land-use and resource-leasing decisions of the department.

And while most of Mountain States' litigation has occurred in the West, the foundation is active elsewhere as well. In one of its most recent actions, three days before Reagan announced his selection of Watt, the foundation filed a brief in support of Virginia strip-miners' efforts at the Supreme Court to overturn portions of the federal strip-mine control law.

The amicus curiae brief was submitted under the name of Watt and two of his foundation associates. As interior secretary, Watt would oversee strip-mine enforcement through the Office of Surname Mining.

Watt, 42, a onetime senatorial assistant, held key positions in the Interior Department during the nixon and Ford administrations and was vice chairman of the Federal Power Commission before leaving in 1977 to head the foundation.