Energy Secretary James R. Schlesinger Jr. yesterday unveiled regulations that would force new utility and industrial boilers to burn coal instead of oil or natural gas to reduce U.S. dependence on energy imports.

At the same time, however, Schlesinger said that the Department of Energy would urge industrial and some utility users who have switched from natural gas to oil to switch back to usiing natural gas if possbile, because domistic gas supplies are so plentiful.

Both actions are targeted at carrying out the intent of the National Energy Act, signed by President Carter last week. The act seeks to increase the production and use of domestic energy, including both coal and natural gas, and reduce dependence on foreign oil.

Schlesinger said the new coal use regulations "are tough and are intended to be tough" and would save from 300,000 to 500,000 barrels of oil a day by 1985. DOE has said that even with the National Energy Act the United States will be importing about 10 million barrels of oil a day by the mid-1980s.

The proposed regulations would require new plants to burn coal unless they could prove that the cost of alternative fuels would be signifiently cheaper. There are other provision for exemptions under environmental or financial conditions that would make coal-burning impractical.

Carter's original proposals for increased coal use, including an industrial user tax on oil and natural gas that was rejected by Congress, would have saved more than 2 million barrels of oil a day by 1965, the administration claimed.

DOE officials said they won't try to force plants that have converted from natural gas to oil to shift back, but Schlesinger said they would encourage those plants to do so.

The plants were encouraged to shift from gas to oil when domestic supplies were short and residential users were threatened with interruption of service.

In a sense, DOE's short-term program to increase the industrial gas use, and long-term program to replace natural gas for industrial boilers, as spelled out in the law by 1990, are contradictory.

What Schlesinger says he hopes to do, however, is to get industrial users who have shifted from natural gas to oil since 1973-1974 to go back to gas in the near term to sop up some of the natural gas surplus that is clogging domestic markets. This would also reduce some of the estimated 3.5 million barrels of oil imports a day that have been attributed to major cuts in industrial gas consumption.

Schlesinger said the current gas surplus, which many oilmen are calling a "gas glut," amounts to 1 trillion cubic feet of gas. This gas, available previously in the intrastate market, where prices are higher, is available to the interstate market bacause of the increased prices allowed under the Natural Gas Policy Act.

Because of the improved supply situation, as contrasted to the winter of 1977, Schlesinger said there is little likelihood that there will be a shortage of either natural gas or propane this winter.

At a news conference held in DOE's Forrestal Building, Schlesinger said, "We are pleased to see the restoration of authority in Iran" and that he expects full production from the Iranian oil fields to be restored in a few weeks.

In recent weeks, the lost production from Iran has been made up in large measure by increased production from the other Persian Gulf countries, most notably Saudi Arabia, which has boosted its production from about 7 million barrels a day before the troubles in Iran to more than 10 million barrels a day.

On the other energy questions, Schlesinger said:

DOE will "take vigorous action" to increase revenues for producers who have so-called "marginal wells" that could also lead to increased production. This measure was aggressively pressed by Ron Jim Wright (D-Tex.), and will go into effect in the next months.

The administration will propose the decontrol of gasoline prices when the new Congress meets. Decontrol was initially proposed by Carter in April 1977, but the Energy Department held bcack on decontrol because of fears that it would undercut lobbying to win enactment of the energy bill.

Declined to say why the White House had invoked executive privledge on DOE statements that a prolonged coal strike earlier this year could have resulted in 3.5 million unemployed in the east central states.

Said that "there is some tension" between President Carter's commitment at the Bonn economic summit to raise domestic oil prices to the world level by 1981 and the administration's new anti-inflation program.

Said about his remaining as energy secretary, in response to a question, "It is my intentions to stay on, and I have set no date" to leave.