The NYPD will be beefing up security with an army of police officers at Ground Zero for the opening of the WTC memorial this fall.

About 200 police officers will be stationed at a downtown command post by July.

“Common sense dictates that we have to be concerned about a possible act of retaliation as far as the death of [Osama] Bin Laden is concerned,” Police Commissioner Ray Kelly said today, referring to the terror chief killed by Navy SEALS last month.

Several hundred more officers will added incrementally as new buildings are constructed, Kelly added.

The 9/11 Memorial Plaza is scheduled to open on the 10th anniversary of the attacks this year and should prompt flocks of visitors.

It will take up 8 acres and include two cascading waterfalls and reflecting pools.