Electrical workers at the White House may be tracking cancer-causing PCBs through portions of the Executive Mansion and the Old Executive Office Building in the dust on their shoes and clothing, the Environmental Protection Agency said yesterday.

An analysis of air and dust samples taken July 31 by a team of EPA experts showed that seven transformer vaults -- including one beneath the north portico of the White House that once housed PCB transformers -- contain PCB contaminated dust and that some of it may have been tracked outside the vaults.

J. Stephen Dorrler, head of an EPA environmental response team that conducted the tests, said there apparently is no immediate health hazard posed by the dust. He said the results of a second series of tests performed Wednesday in hallways and stairwells in the Old Executive Office Building and the Executive Mansion will determine how widespread the contamination might be.

In the July 31 tests, Dorrler said, "We took some samples of dust from door sills at the vaults which would indicate that we have a trackage problem." Based on the results of those tests, he said, "we are now looking to see . . . what is the extent of the contamination."

PCBs, or polychlorinated biphenyls, were once the most commonly used coolant for high-voltage transformers because of their fire-retardant properties. Laboratory tests, however, showed that PCBs cause cancer, and their manufacture was banned in 1977.

Experts say that the same properties that made PCBs so useful as a coolant are also the properties that make them so dangerous, because it can take decades for PCBs to break down in the environment. In addition, when PCBs are superheated in a fire, they give off deadly fumes, including dioxins, which the EPA has called "one of the most toxic substances known to man."

The tests at the White House complex were ordered after the EPA and the General Services Administration discovered leaks in two PCB transformers during a July 29 inspection there, Dorrler said.

White House spokesmen said the two leaking transformers were found in a vault beneath West Executive Drive, which runs between the White House and the Old Executive Office Building. They said the leaks were sealed the next day.

GSA spokesman Dale Bruce said yesterday that there are no PCB transformers in the Executive Mansion. "We want to emphasize that there is not now, nor has there ever been, any danger to President or Mrs. Reagan or any occupants of the White House," he said.

Bruce said that about two years ago, two transformers in the White House that had contained PCBs were "retrofilled," a process in which the PCBs are drained and replaced with a nontoxic coolant.

Dorrler said that dust samples taken from that vault beneath the north portico indicate there are still PCB remnants inside, and that "there is some movement of the dust out of the vault, but in levels not to be considered a health hazard."

Some dust and air samples in five PCB transformer vaults in the Old Executive Office Building show significantly higher levels of PCB contamination, Dorrler said. "We're not saying it's a health hazard . . . . What we're saying is that it's a cause for concern."

GSA spokesman Bruce said that the two PCB transformers under West Executive Drive and 17 more in vaults in the Old Executive Office Building will be retrofilled on a "priority basis" starting Monday night.