What is the protocol for US Soldiers who are greeted by foreign Heads of State?

SSG(P) (Join to see) wow it's been a minute, but always start out with the REGULATIONS. I found the following information:

Military courtesy AR- 600-20 ARMY COMMAND POLICY AND AR 600--25 LOOK AT CHAPTER 2.

https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/ARN20654_R600_25_Admin_FINAL.pdf

a. Courtesy among members of the Armed Forces is vital to maintain military discipline. Respect to seniors will be extended at all times (see AR 600–25).
b. The actions of military personnel will reflect respect to both the national anthem and the national colors. The courtesies listed in AR 600–25 should be rendered the national colors and national anthem at public events whether the Soldier is off or on duty, whether he or she is in or out of uniform. Intentional disrespect to the national colors or national anthem is conduct prejudicial to good order and discipline and discredits the military Service.

https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/r600_20.pdf

Maj Marty Hogan SPC Margaret Higgins COL Mikel J. Burroughs CPL Dave Hoover Lt Col Charlie Brown Lt Col John (Jack) Christensen SCPO Morris Ramsey TSgt Joe C. PVT Mark Zehner Sgt (Join to see) SSG Michael Noll SSG Robert Mark Odom CPL Douglas Chrysler PO1 Tony Holland SGT Steve McFarland SPC Mark Huddleston PO3 Craig Phillips CW5 Jack Cardwell PO3 Phyllis Maynard

There is a protocol office on you base, go there.

I would recommend you see if there is a Protocol office on the base. The ones that deal with dignitaries. Usually the 3 shop for the base would be a good start. Get their input.

I highly doubt you will run into a Head of State without a sufficient heads up to include a brief on proper protocol.

But Mr. President and Sir would both be appropriate and sufficient. I served 3 1/2 years on Embassy Duty. Meeting muckedy Mucks isn’t that dramatic. Just be polite and don’t over think it

Almost always, the more formal you are, the better. A head of state should be treated as a head of state.
But such a visit would be planned and staffs from the CoS and your military protocol officer will get such matters settled before any such visit.

I pulled this from AR 600-25: Salutes, Honors, and Visits of Courtesy:

Chapter 2
Personal Salutes and Honors
2–1. Honors
c. Foreign military officials listed in table 2–1, holding positions equivalent to those of DOD and military department officials, both military and civilian, will be rendered the honors to which the equivalent U.S. official is entitled, regardless of actual military rank. All other foreign military persons will receive the honors due their actual rank or its U.S. Army equivalent.

While this is meant to cover things like guns, ruffles and flourishes, I would interpret it to also apply to saluting and addressing the official.

Note that:
Chapter 1
General
1–5. Hand salutes and salutes with arms
e. It is customary to salute officers of friendly foreign nations when recognized as such. The commanding general, U.S. European Command; the commanding general, U.S. Army Europe and Seventh U.S. Army; commanding general, U.S. Forces Korea and Eighth U.S. Army; commanding general, U.S. Army, Pacific; and commanding general, U.S. Army, Southern Command, are delegated the authority to establish policies for recognition courtesies prevailing locally for foreign officials. Should inactivation eliminate any of these commands, the authority will pass down to the next level of command. This authority will not be delegated further.

As others have mentioned, if you can find a protocol office, I am sure they will have the specifics. I bet the G3 of the highest echelon on the base will also know the protocols because they are staff of the level that will be most involved in dealing with the visitor.

When in doubt, there is nothing wrong with Saluting while in uniform and coming to attention and addressing "Sir/Ma'am" when addressing the individual.

An excellent question. Civil affairs should give you a briefing. If your unit doesn't have a civil affairs shop, ask the S-2. I can't give you a definitive answer because it depends in which country you are. I served in The Marine Security Guard Battalion as the OpsO for Sub-Saharan Africa. What would get you in hot water in one country, could be common courtesy in another. Most career diplomats and foreign military are pretty forgiving, and will help you out to prevent any further embarrassment. But some foreign dignitaries and bureaucrats can be real pricks. Gross generalization... the bureaucrats are usually the worst.

Do not do the obama bow, but stand tall, embassy should give proper protocol

I would hope that the command structure would be aware of such a visit, ahead of time, and brief everyone on base on the protocols required.

Your actions depend on the environment. Your local leadership will receive protocols in each instance. Have no fear,?your unit will tell you what to do.