When grounding a striker fire pistol like M&P or Glock (with no external safety), do you have to drop the mag and clear the chamber or does the internal striker safety count as the engaged safety per safety condition 1?

Set it down and go!  It IS on safe when not in ones hands.

Yes, when in doubt, ask the RO during course readthru or prior to the make ready command

i AM the RO. i need clarification on this rule.

I did not stutter, but perhaps I was not clear enough.

In every Major match I have shot in the last dozen years.
Pistols without factory external safeties are OK to abandon loaded. (i.e. on safe by default) or empty.
Pistol with external safeties will be placed on safe (manually) or unloaded.

Of course any local dirt shoot can dream up any rules the match director wants so the above may not apply.

USPSA Rifle, Shotgun and Multigun Rules (provisional) January 1, 2013

3.3.6 Within the context of a Multigun stage, a competitor may be required to “abandon” a firearm in order to use another firearm. In this context, an “abandoned firearm” is a firearm which the competitor has used, placed in the provided retention device in accordance with course requirements, and subsequently moved more than one (1) yard away from.

3.3.6.1 An abandoned firearm must be in applicable ready condition (see Section [3.1]) or empty with no ammunition anywhere in the firearm.

3.1.3 Autoloaders (treat all Rifles and Shotguns as “Single Action.”):

3.1.3.1 “Single action” – chamber loaded, hammer cocked, and the safety fully engaged (if the firearm is designed to have one).

3.1.3.4 With respect to Rules [3.1.4.1] and [3.1.4.3], the term “safety” means the primary visible safety lever on the firearm (e.g. the thumb safety on a “1911” genre handgun). In the event of doubt, the Range Master is the final authority on this matter.

Since Glocks have three internal safeties and not designed to have an external safety, condition is met by putting it into the provided retention device.  If an M&P has an external safety (some can/do) then the safety should be engaged and put in the provided retention device.

Mag dropped, chamber cleared would also work.

Modify See RO to See CRO or Match Director.  Who should be involved if its a DQ situation.

In all reality every match can have its own set of rules. As stated pretty much every match allows you just set it down as is and GTG. However it is best to check the rules or ask the RO at the match you are at. Telling the RO that a bunch of guys on the Internet told you so usually isn't a good enough excuse for breaking a rule.