Rep. Mike Synar (D-Okla.) said yesterday that a senior official at the Environmental Protection Agency may have ordered erasures of items on his appointment calendars after Synar requested them, but the EPA dismissed the allegation as unfounded.

Synar, chairman of a House Government Operations subcommittee, last week requested the calendars, telephone logs and other records of John A. Todhunter, EPA's assistant administrator for toxic substances and pesticides. At Synar's request, aides to EPA's acting inspector general, Charles Dempsey, secured the calendars in Todhunter's office late yesterday.

In a letter to Dempsey, Synar said he had "received information alleging that Dr. Todhunter had instructed his secretary to erase entries on his appointments calendars prior to their delivery to this subcommittee and to cancel appointments already scheduled with industry representatives for the next week."

An EPA spokesman said Todhunter, on the advice of EPA lawyers, routinely has destroyed his appointment calendars every month for the past year. He denied there were any erasures on the calendars for January and February of 1983, which had not yet been destroyed.

The spokesman said the calendars "are often inaccurate and misleading because some meetings don't take place. There's no effort to hide anything, nothing illegal or unethical. These people in Congress are grabbing at every last headline."

Todhunter's calendars became an issue last spring after they were obtained by then-Rep. Toby Moffett (D-Conn.), who criticized Todhunter for holding frequent meetings with chemical industry officials before making major decisions on the regulation of asbestos and formaldehyde.

Todhunter held private meetings, often over breakfast or dinner, with representatives of the Chemical Manufacturers Association, Formaldehyde Institute, Monsanto Corp., Ciba-Geigy, Dow Corning, Mobay Chemical, Reilly Tar and Chemical and the Synthetic Organic Chemical Manufacturers Association. He had 16 such meetings with industry officials in January and February, 1982.

In another development, congressional sources said a House Public Works subcommittee chaired by Rep. Elliott H. Levitas (D-Ga.) has been told that some EPA documents it is seeking may have been destroyed or removed from agency files, possibly by high-level officials. The sources said the subcommittee is hiring more investigators to look into the allegations.