Interior Secretary James G. Watt yesterday formed a five-member commission to investigate accounting losses and what he called "outright theft" of oil that may be costing the government and Indian tribes millions of dollars a year in mineral royalties.

The Justice Department, the FBI and other federal law enforcement agencies have been investigating the alleged losses for years. At least one federal grand jury also is looking into oil thefts on federal and Indian lands.

But Watt said "little has been done" by past Interior Department administrations to handle "the serious allegations of waste and revenue losses."

The commission, headed by University of Illinois Prof. David F. Linowes, will report back to Watt within six months. Linowes indicated that the bulk of the royalty losses, which affect federal, state and Indian revenues, apparently come from faulty and perhaps intentionally defective accounting procedures.

Linowes estimated that the losses range between 7 and 10 percent of the $4 billion in royalties due annually on the leases. He and Watt said the problem could be exacerbated if oil revenues increase as expected to $6 billion next year and eventually to $20 billion a year.

When questioned at his press conference, Watt, who has been under increasing attack lately from environmentalists and some Democratic congressmen, dismissed as "hilariously funny" a poll by the 4.5 million-member National Wildlife Federation which expessed strong disapproval of his environmental and resource policies and led the nation's largest conservation group to ask President Reagan to fire him.

Watt implied that the poll misrepresented his policies. He said he answered the poll's first question, and "I voted to dismiss Secretary Watt." Asked if he was saying the poll was rigged, he replied: "Well, it sure fooled me, didn't it?"

The Wildlife Federation is considered one of the country's more conservative conservation groups. Its action Tuesday came in the wake of a petition drive by the Sierra Club and heightened activities by other environmentalist groups aimed at removing Watt.

Watt once again flatly denied that the White House, concerned about growing political problemns with his policies in the West, has told him to ease up. He said he would be "surprised" if he ever received such word from the White House.

Watt said he did not view himself as a political liability. Instead, he said, he was carrying out the promises of the 1980 Republican platform.

Yesterday, Watt also formally approved an amended five-year offshore oil leasing program which will open about 1 billion acres of land to potential exploration between 1982 and 1986. He declined to give a new timetable for a final decision on a Northern California lease proposal which has been hung up in political controversy since last spring.