President Carter, saying he was deeply concerned" over reports that some White House staff members used drugs illegally, warned yesterday that any staff member discovered doing so in the future will be fired.

But White House press secretary Jody Powell said there would be no White House investigation of the drug use allegations because he knew of "no reasonable way to conduct" one.

The president dispatched a tersememo to his 11 senior staff members stating that he expected "every member of the staff to obey the law. Whether you agree with the law or whether or not others obey the law is totally irrelevant."

"You will obey it," he wrote, "or you will seek employment elsewhere."

"I expect that you will convey my feelings directly and in no uncertain terms to every member of your staff," the president said.

The presidential admonition was in part an attempt to close one of the strangest and most embarrassing chapters in recent White House history.

It began last Wednesday with the news that presidential drug policy adviser Dr. Peter G. Bourne had written a prescription for 15 Quaalude tablets using a phony name for the aide who sought the drug. Bourne resigned the nexg day, but he was quoted as saying that there was a "high incidence" of marijuana use, and some cocaine use, among White House staff members.

Reporters then began telephoning White House staffers at every level to seek to substantiate Bourne's comments. A handful of staff members reportedly said they did use marijuana.

Finally, the president himself was quoted as saying he was "sure many people smoke marijuana but I'm not going to ask about it." Carter made the comment which Powell said was not in reference to White House staffers, as he stood backstage at a country music concert Friday night at the Merriweather Post Pavilion in Columbia, Md.

Carter was unaware that a reporter, Stuart Levitan of the Madison (Wis. Press Connection, was there at the time. Levitan, incidentally, later said that at the time he had just smoked part of a marijuana cigarette.

On Saturday, Powell charged that the press was engaged in a hypocritcal "witchhunt," a comment that brought him a lecture from the president yesterday.

The president "did not want the impression conveyed that either he or I felt that whatever standard of conduct might be observed by members of the press justified such behavior by members of the White House staff," Powell said.

Powell said the president understood "the statistics" about marijuana use - that tens of millions of Americans use it. But he said "you can't live your life like a private citizen if you're going to work here."

Two congressional leaders commented yesterday on the White House drug controversy.

Senate Minority Leader Howard H. Baker (R.Tenn.) called for an inquiry into reports of drugs use among White Houses aides. "We need at least a fuller explanation," Baker said.

House Speaker Thomas P. O'Neill Jr. (D-Mass.) said that anyone "found with pot in my office goes out the door."

Many persons contacted in the White House and on Capitol Hill privately have criticized the press coverage of the "high incidence" of marijuana use among reporters.