Joe Biden‘s Los Angeles fundraiser is already attracting protests, and while law enforcement’s not trying to be combative, they’ve got a message for protesters … don’t step out of line.

We spoke with sources in law enforcement who tell TMZ they’re both ready for anything … placing the president’s safety as their highest priority.

A Secret Service official tells TMZ … they plan meticulously for every scenario, and they’ve got a plan layered with redundancies to ensure President Biden’s safety.

The basic premise, we’re told … LAPD will protect against disruptions to the venue and will patrol the outside of the spot in Downtown L.A. while Secret Service handles security inside. However, any serious threat would fall under the Secret Service’s purview.

As for the LAPD … a source with the force tells us there have been no threats made against the event, but protests pop up all the time in Los Angeles, and they expect Saturday to be no different.

We’re told they’re going to let protesters demonstrate so long as it stays peaceful, but they’re ready to break up the crowd the moment they step over the line and will arrest people if need be.

Posts are already going around social media encouraging people to come out and demonstrate against Biden — specifically for his support of Israel during their incursion of Gaza … so, it’s safe to assume protesters will be out in full force.

As we told you … Biden’s already raised $28 million from the H’wood community — a staggering sum given the event doesn’t kick off until this evening.