Claiming that one of its employees may be involved in an illegal conflict of interest, the National Oceanic and Atmospheric Administration (NOAA) has withdrawn its sponsorship of a McLean woman's attempt to make the first nonstop balloon crossing of the United States.

The flight, originally scheduled to begin Aug. 20, has been delayed repeatedly because of bad weather. NOAA's action, disclosed yesterday, is not expected to force cancellation of the flight.

A NOAA spokesman said the government agency is pulling scientific instruments off the balloon because a NOAA employe connected with the flight may have used "his position or the influence of his position for his personal gain."

Although NOAA spokesman Albert Mark refused to name the employe involved or explain the nature of the alleged conflict of interest, he said the employe "should have known better" and that NOAA's lawyers are conducting an investigation.

The employe under investigation, according to sources close to the balloon flight, is Dr. Rudolf J. Englemann, an environmental scientist from Boulder, Colo.

Englemann, 49, who is the project director of the balloon flight, said yesterday he has been told by NOAA not to comment on the investigation.

McLean balloonist Vera Simons, however, said yesterday that she was "appalled" at the government's withdrawal from the balloon flight, which is also being sponsored by nine major aerospace firms and the Seven-Up Bottling Company.

"I cannot believe that NOAA would take this precipitous act without investigating the facts," Simons said.

But NOAA spokesman Mark said, "We felt the only way to be clean about this was to pull out our equipment."

NOAA had planned to place sophisticated instruments capable of measuring changes in air pollutants, ozone levels and radiation aboard Simons DaVinci TransAmerica.

Simons argued yesterday that NOAA is doing the public a disservice by halting research into the nation's lower atmospher that could prove valuable in controlling air pollution.

NOAA instruments were used in 1976 aboard an earlier flight of the DaVinci balloon. Information gathered on that flight over St. Louis has been used by the federal government in studies of the movement of urban air pollution.

Mark said yesterday that while the agency's investigation of a possible conflict of interest does not involve "a great deal of money" it is looking into "the whole idea of someone using his positions at NOAA for commercial gain outside the agency."

Mark said NOAA's withdrawal of sponsorship, valued at about $28,000, is not meant to stop the balloon flight but to keep the federal government out of the project "as long as there is the slightest prospect of any irregularity."

The helium balloon, which is larger than the Goodyear blimp, is scheduled to leave the Oregon coast sometime this month-- as early as Monday-- and travel 2,205 miles to a landing near Norfolk, Va.