A U.S. District Court jury yesterday found the owner of a local stenographic company guilty of overbilling the Reagan administration for transcribing presidential news conferences and other work.

The jury deliberated about six hours before finding Richard Lee Boyd, 31, of Bowie, and his company, North American Reporting Inc., guilty of 16 counts of mail fraud and making false statements in filing the inflated bills. Law enforcement officials said the overbillings on those charges amounted to more than $10,000.

Boyd's firm had contracts with the government during the last year of the Carter administration and the first year of the Reagan administration to record and transcribe White House presidential and other press conferences, and do other stenographic work. The material was for government publications and public use.

A federal grand jury indicted Boyd and the company last February on eight counts of mail fraud and eight counts of making false statements between February and September 1981. The grand jury charged that Boyd had submitted false billings that included the names of employees who had not performed the work, an inflated number of hours worked and non-existent overtime hours.

U.S. District Court Judge June L. Green said she would sentence Boyd on Sept. 8. Special Assistant U.S. Attorney Harriet McFaul said Boyd faces a maximum of 80 years in prison and fines of $88,000. His company also faces maximum fines of $88,000.