Donald Trump's going from wildfires to wild winnings ... 'cause he's already traded in L.A. for L.V. -- stopping for a speech at a popular Las Vegas casino.

The POTUS hit up Circa in downtown Vegas Saturday for a speaking engagement ... and, he even stopped on the casino floor -- waving to a crowd of cheering gamblers who chanted "U.S.A." for the newly minted 47th president.

Check out the clip ... tons of smiling workers want to shake DJT's hand -- and, the Secret Service does an admirable job keeping the crowd from closing in on DJT.

The purpose of Trump's visit was to speak to an assembled crowd of Nevadans ... cheering him on while he talked about his policy to eliminate taxes on tips for employees in the service industry.

Of course, Sin City runs on tips ... so, ya gotta think a ton of workers in Vegas are stoked the president's trying to help them keep a few more dollars in their pockets.

President Trump's on a whirlwind trip on the West Coast ... stopping briefly in L.A. to meet with California Governor Gavin Newsom and Los Angeles Mayor Karen Bass about the devastation caused by wildfires in the region this month.

Trump and Newsom promised to work together on rebuilding efforts ... despite the tension between the two politicians.

BTW ... there's a whole lot of activity in Vegas this week -- with thousands flocking to the city for the AVN Awards -- the Oscars of porn.

It's unclear how long DJT will be in Vegas for ... but, with some huge NFL games tomorrow, he may want to send a Secret Service agent down to make a couple bets!