The President's Commission on Coal has concluded that coal could by 1990 replace up to 2 million barrels of oil used daily to generate electricity and the changeover could be accomplished in full compliance with the strictures of the clean air act.

In a report to be released tomorrow, the commission, citing major differences in the safety records of larger coal companies, also called for an immediate investigation by the National Academy of Sciences of the factors that distinguish the safest from the most dangerous mines.

The commission's staff found a seven-fold difference in the incidence of disabling injuries among the 20 largest coal companies with underground mines.

United States Steel Corp., the fourth largest producer, which operates 28 underground mines, had the best record between January 1978 and June 1979, with only 3.02 injuries resulting in a lost day of work for every 200,000 hours worked.

The eighth largest producer, Westmoreland Coal Co., with 29 underground mines, had the worst record among the 20, with 21.01 such injuries per 200,000 hours.

Even greater differences were found when all 559 underground mines employing 50 persons or more were grouped not by company but by safety records. About one-fourth of the total production came from 193 mines with a rate of disabling injuries of only 2.86 per 200,000 hours worked. At the other end of the scale, 31 percent of total production came from 211 mines with an average injury rate of 17.46.

"Underground coal mining," the commission said, "is the most hazardous occupation in the United States." While fatalities were sharply reduced after passage of the 1969 Mine Safety Act, the rate of disabliang injuries has been rising since 1975 and last year the fatality rate rose as well.

As a group, smaller mines are less safe than larger ones, the commission noted, but added that the wide variation in injury rates in larger mines "strongly suggests that in some mines, operators, miners and federal inspectors are working together to insure safety, and in others they are not."

The commission was appointed by President Carter nearly two years ago following a major strike by union miners. Its primary mission was to recommend ways to improve labor-management relations in the industry.

Since then labor problems have simmered down, the commission said, with the time lost because of wildcat strikes falling dramatically. In 1977, 2.3 million workdays were lost due to wildcat strikes, but only 546,000 in 1978 and 1979 combined.

Regarding consumption, the commission specifically proposed that utility use of oil and gas to generate electricity be reduced to 40 percent of present levels by the end of the decade. In industry, the commission wants any large new boilers to use coal beginning immediately, and would require any large existing units that can burn coal to do so after 1985.

The cost of converting utility boilers to coal and of constructing new coal-fired units should be shared nationally "in order to ease the burden on electricity consumers," the commission said.

"To keep electricity rates from rising above what would occur with continued oil and natural gas use, federal grant assistance of up to $15 billion should be provided," it recommended.

The Carter administration is expected shortly to propose legislation to provide assistance to utilities that must convert to coal. The nature of the assistance and the sort of strings attached have made this bill highly controversial. on two occasions when it was about to be unveiled, the administration pulled it back for further study.

"New coal-burning power plants built under the Clean Air Act's new source performance standards will cause in most instances no more, and generally fewer, sulfur dioxide, nitrogen oxide and particulate emissions than most existing oil units," the commission declared. "The replacement of older oil units with new, relatively clean coal units allows increased reliance on coal with no net increase in environmental and health-related emissions."