I have applied for a B1/B2 US visa, got approved during the interview and was informed the next day that my visa application has been put into an administrative processing. My question is, since I also hold another passport that qualifies for ESTA, can I apply for an ESTA while my B1/B2 application is pending with another passport?
There doesn’t appear to be a rule that says you can’t apply for an ESTA while a B visa is processing. You could try and see if it is approved.
The only risk is if your B is denied then your ESTA becomes invalid, even though it’s on a separate passport.