The actor waived his appearance that was set for Thursday morning, where he was due to beam into a courthouse in Santa Fe County and tell the court how he feels about the involuntary manslaughter charge that was re-filed against him in recent weeks.

Instead, he just submitted a not-guilty plea through his attorneys ... opting to pass on a virtual pop-in. Makes sense -- he's already telegraphed his game plan, signaling through lawyers that he wants this all done quickly and out of the spotlight.

Remember, Alec made clear last week that he has the right to a speedy trial ... emphasizing the fact he does NOT want to drag this out any longer than it needs to be. There are some conditions of release he has to abide by too -- no consuming booze, no illegal substances and no firearms and no leaving the U.S. without written permission ... the usual.

Now, that he's pled not guilty ... the case can continue, and he'll eventually have to come to court for the trial itself. Considering Alec has been denying any wrongdoing from the start -- all signs point to him fighting this thing to the very end, in front of a jury.

Alec has gotten some support lately on this front -- specifically, from SAG-AFTRA ... which put out a statement saying it's not an actor's job to check firearms on set.

Remember, the D.A.'s office there already tried prosecuting him once -- but dropped the charges ... only to resurrect them again through a grand jury, presumably on newer evidence they think makes their case solid.