The Eagles are setting the tone for the upcoming benefit concert for Los Angeles wildfire victims with a massive first donation ... pledging over seven figures.

TMZ has learned ... the famous rock band is donating $2.5 million.

It's unclear if the huge donation means the Eagles are among the acts performing later this month at the FireAid benefit concert.

As we first told you ... there's been an overwhelming response from musicians who want to participate, with over 50 bands and performers who want in. There are only 24 slots for now, but organizers are trying to add slots to accommodate more acts.

We've been told the performers are going to be Los Angeles based ... and it's worth noting the Eagles were formed in L.A. in the 1970s and one of their biggest hits is "Hotel California."

FireAid is going to be engaging, exciting and will raise a ton of money ... and the Eagles are getting the ball rolling here.