Kourtney Kardashian and Travis Barker are clearly still in their newly-engaged phase … spotted on the beach with some serious PDA.

Eyewitnesses tell TMZ … the make-out couple was staying at the Montage Resort in Laguna Beach. After leaving the pool Tuesday, lips locked, they hit the sand for more action … drawing attention from beachgoers within eyesight.

Kourtney was straddling Travis … his hands pulling her jeans down a bit, and sucking faces like there’s no tomorrow! Things got so intense, one nearby family — with kids — walked up to them, although it’s unclear what was said, but probably something along the lines of “get a room!”

After their sandy sesh, the two ran down to the ocean for more fun … and to cool off.