The House Intelligence Committee has started an inquiry into what it says are a number of foregeries evidently designed to give U.S. intelligence agencies a black eye around the world.

Committee officials said the most recent example was a purported secret "annex," or supplement, to an unclassified Army field manual. The supplement, stamped "Top Secret," calls for Army intelligence units in friendly countries to infiltrate insurgent movements and eben to sponsor "violent" actions when those governments "show passivity or indecision in the face of communist or communistinspired subversion."

The 13-page typewritten supplement, ostensibly approved in 1970 by then-Army chief of staff William C. Westmoreland, was reproduced in the most recent issue of the Covert Action Information Bulletin, a magazine started here several months ago to expose CIA and other U.S. government intelligence operations and personnel.

One of its editorial staff members, Louis Wolf, said they felt the document was genuine, partly because of its format and style, partly because it was cited or published in several countries before U.S. officials disclaimed it.

The chief counsel of the House Intelligence Committee, Michael J. O'Neil, agreed yesterday that "it's very well done," but the committee had satisfied itself that it was a forgery which first appeared in Bangkok in 1976 and most recently last week, in a newspaper article in Copenhagen.

"There have been a number of other forgeries since 1976 that we've become aware of," he added. "Some purport to be State Department documents, some Defense Department documents. What we're interested in determining is whether there are any common themes behind them and, since they appear to be of rather high quality, we're interested in who could do them."