White House officials attempted more than a year ago to dismiss James W. Sanderson, an adviser to Environmental Protection Agency Administrator Anne M. Burford, because of allegations that he was involved in policy decisions affecting a private firm he represented, senior administration officials said yesterday.

But the effort to oust Sanderson failed because Burford repeatedly insisted that he remain on the job, the officials said.

Sanderson, a Denver attorney, worked as a paid, part-time adviser to Burford from March, 1981, to June, 1982. During that time, EPA officials have said, he participated in several meetings on landfill regulations that affected Chemical Waste Management Inc., a client of Sanderson's that operates several toxic waste landfills.

Sanderson has denied any wrongdoing.

But the allegations about him are being taken seriously by White House officials. One official yesterday described the Sanderson charges as the "real problem" in the EPA controversy. Six congressional panels and the Department of Justice are looking into charges of conflict of interest and mismanagement in the agency.

Specifically, White House officials said the allegations about Sanderson's conduct may cloud Burford's future. So far, President Reagan has insisted on supporting his embattled EPA chief, but administration officials said that support could change if the allegations about Sanderson prove true.

The effort to oust Sanderson came more than a year ago, officials said. C. Boyden Gray, counsel to Vice President Bush, met with several administration officials--including then-White House personnel chief E. Pendleton James and then-presidential adviser Martin Anderson--on the Sanderson matter.

At the meeting, some White House officials expressed concern that Sanderson was taking part in policy deliberations that could benefit his clients. But those who sought Sanderson's ouster were told that Burford would not agree to their demand, according to knowledgeable officials. "She was quite adamant," one recalled.

Gray said yesterday through a spokesman that he could not comment on the matter because the "whole situation is under investigation." Anderson said he could not recall the meeting. James said he recalled such a meeting but did not remember details.

Sanderson was nominated for the EPA's third-ranking job, but he withdrew from consideration last summer after the EPA's inspector general, the Justice Department and congressional investigators began looking into charges that he had influenced an EPA water quality standard that affected another client, the Denver Water Board. The board was seeking permission to relax the standard so that more effluents could be discharged into the water.

Sanderson has maintained that he removed himself from any agency discussions that could have directly benefited his clients, and that he participated only in "broad" policy discussions on landfill regulations.

Even after he left the agency last June, Sanderson continued to have contacts with Burford. In January, for example, he talked to her about a permit for an incinerator ship owned by Chemical Waste Management. The EPA later reversed a staff decision and accelerated consideration of the permit.

Last week, Rep. Mike Synar (D-Okla.), chairman of a House subcommittee investigating the EPA, asked the FBI to investigate charges that Sanderson "violated a federal criminal statute."