Despite President Reagan's unwillingness to fire Environmental Protection Agency Administrator Anne M. Burford, the outlines of a White House strategy that could lead to her resignation emerged yesterday, and presidential aides said privately that she may soon decide to step down.

"The pressure is building," one White House official said.

The strategy that could lead to a resignation is said to include use of a "back-door channel" to urge Burford to step down in the face of continuing Justice Department and congressional investigations into possible wrongdoing at the agency.

Administration sources said yesterday that the president's statement in defense of Burford as he toured a plywood mill in Klamath Falls, Ore., on Saturday had been carefully constructed to avoid discussion of a resignation. Reagan expressed confidence in the embattled EPA administrator and said she could "stay in the job as long as she wants."

Reagan's seemingly offhand statement was said to be the result of a strategy that evolved Friday at a meeting of Reagan and top White House officials in San Francisco. At the meeting, administration sources said, White House chief of staff James A. Baker III and Cabinet secretary Craig L. Fuller sought Burford's removal.

The president declined to fire her but yielded to the entreaties of his staff and agreed to a statement that would, as one official put it, "give her running room to gracefully withdraw."

Neither Baker nor Fuller was available for comment yesterday. Nor was presidential assistant Richard G. Darman, who stayed here last week and reportedly helped engineer support for Burford's removal.

White House communications director David R. Gergen, also known to want Burford out, said yesterday, "I don't know what she's going to do." Gergen said he had not called Burford about her plans because such a telephone call could be interpreted as pressure from the White House.

Another White House official, citing Reagan's comment that Burford could stay "as long as she wants," said he hopes that will not be very long. The official said the president's statement was designed to make it easy for her to resign, if she wants to, by signaling that such a resignation is not necessary to avoid being fired.

A third administration official said Burford may not be easily coaxed into leaving her job. "I think she's going to drag it out," the official said.

Burford "thinks she's been shafted" by the Justice Department decision last week to stop defending her in the battle with Congress over disputed EPA documents, the official added, and thus may resist efforts to bring about her resignation.

An informed White House official said yesterday that a "back-door channel" is being used to communicate with Burford, but declined to elaborate.

Other officials suggested that Burford's mentor, Interior Secretary James G. Watt, would be the most logical official to talk Burford into resigning. Watt, who could not be reached for comment yesterday, has been consulting frequently with Burford about the EPA controversy.

EPA spokesman Rusty Brashear said yesterday that a meeting this week between Burford and White House officials to discuss congressional demands for certain EPA documents is a "possibility." Burford faces a Thursday deadline to turn over documents subpoenaed by a House subcommittee chaired by Rep. John D. Dingell (D-Mich.).

Although there were reports over the weekend that Burford would meet with Reagan today, Gergen said no such meeting is scheduled.

Burford was cited for contempt of Congress in December when she refused--on Reagan's orders--to give another House subcommittee EPA documents on the $1.6 billion "Superfund," established to clean up toxic waste dumps.

Her refusal to turn over the documents was based on a presidential claim of executive privilege, but the Justice Department told Burford last Thursday that it can no longer defend that claim nor represent her or any other EPA officials because it is also investigating allegations of wrongdoing at her agency. Six congressional panels are also investigating allegations of conflict of interest, mismanagement and political manipulation in EPA programs.

The attempt to pressure Burford to resign is reminiscent of situations in which the White House staff has maneuvered for an official's resignation, only to be blocked by the president. The most celebrated case involved Labor Secretary Raymond J. Donovan, whom Baker wanted to fire as a political liability. Donovan went directly to the president, who decided to keep him.

Burford's fate may depend, as did Donovan's, on her ability to ignore White House staff pressure, knowing that Reagan has never liked firing anyone.

But some White House officials said yesterday that they see a difference in Burford's case.

Donovan was relentlessly loyal to Reagan, they said, while Burford was, in their view, insubordinate in telling EPA aides that she felt free to make the previously withheld EPA files available to Congress. Burford made this statement after the Justice Department refused to continue to defend her.

Burford's allies have presented her action as a logical response to a Justice Department that she saw as abandoning an executive privilege claim it had urged her to undertake.

It is not known whether Reagan was bothered by Burford's action. But officials said yesterday that he is concerned about the increasing number of news reports criticizing the EPA, and some White House staff members expressed concern that further disclosures from the current investigations will force Burford out.

Paradoxically, news stories and televised reports predicting Burford's ouster may have contributed to keeping her in office.

Reagan is known to be sensitive about appearing to act in response to media criticism, and CBS and NBC reported this weekend that Burford appeared to be on her way out.