Sasha Obama is working for the summer -- or at least a very small part of it -- at a restaurant on Martha's Vineyard.

Sasha is checking out customers at the register and bussing tables at Nancy's ... a seafood restaurant. Of course, the 15-year-old employee comes with her own entourage.

She reportedly was accompanied by 6 Secret Service agents, who gave her room to work ... sitting outside the popular tourist eatery while she put in her time -- about 4 hours a day.

This won't be a long-term gig. She's just working this week until the rest of the Obamas arrive for a 2 week vacation.