The first Beetle Bailey comic strip was not renewed by King Features Syndicate in 1977 and was also not even renewed under "King Features Illustrated."
Beetle Bailey didn't go to the military until 1951, which that strip also was not renewed alongside the debut of on and off again nemesis Snorkel. However this early strip featuring a college-aged Beetle shows how Mort originally intended the strip.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.