WASHINGTON — Four years ago, law enforcement officials overseeing President Obama’s first inauguration were concerned primarily with keeping the new president safe amid rising threats and nearly 2 million spectators packing the Mall.
This year, the conversation has turned largely to balancing the need for a heavy police presence with ensuring that the crowd gets where it needs to go — and has fun — even if people have to be scanned airport-style to reach the parade route.
‘‘The main focus is to make sure that people enjoy the event without feeling the security is overbearing,’’ D.C. Police Chief Cathy L. Lanier said Tuesday.
For the 2009 inauguration, the Secret Service ordered five extra tons of bulletproof glass, its largest-ever order of ‘‘transparent armor,’’ as preparation for possible danger.
This year, said FBI special agent Debra Evans Smith, acting assistant director of the Washington field office, there are ‘‘no credible threats against inaugural activities.’’
Law enforcement officials from six leading agencies overseeing security at the inauguration, parade, and balls briefed reporters last week on the sensitive security preparations at a secret joint command post in suburban Washington.
Starting Sunday and running nonstop through Tuesday, representatives from 42 agencies — mostly police and military, but also from public works and state highway agencies in the District of Columbia, Virginia, and Maryland — will camp there to watch over festivities and coordinate responses to threats, emergencies, water main breaks, and traffic accidents.
They will work in front of detailed digital maps of the US Capitol grounds positioned in front of an arena-like room, along with live feeds from thousands of traffic and surveillance cameras.
Authorities declined to discuss details such as ‘‘threat levels’’ faced by those protecting the president. In 2008 and 2009, security officials worried about the large crowds Obama drew across the nation — sometimes tens of thousands more people than expected — and reported sending about 4.3 million people through metal detectors during campaign events, nearly double the number from 2004.
In the briefing, police chiefs took turns promising that they’ve learned from mistakes four years ago when ticketholders were stranded in the Third Street tunnel, unable to reach the inaugural ceremony.
The tunnel will be closed. Beyond that, police said there will be more signs, more people to direct visitors, more officers on social media sharing news and information, and smartphone apps to help deliver ticketed people to their seats with Global Positioning System data. The Secret Service is now on Twitter.
‘‘We recognize the need to get people to where they have to go,’’ said Ed Donovan, a Secret Service spokesman.
Police nevertheless warn that there will be checkpoints and road closures and urge people to come early, prepare to stand for hours in the cold, and study inaugural websites to know what they can and can’t bring: Thermoses are prohibited on the parade route, for example, and strollers are not allowed for those with tickets on the Capitol grounds.
Officials have posted lists of prohibited items on the Secret Service’s inaugural website.
Authorities declined to estimate the potential size of the crowd.
Officials have said they are expecting less than half the number of people who came in 2009, drawn in part by the historic swearing-in of the nation’s first black president. Four years ago, 10,000 charter buses headed to Washington. This year, 800 have registered Lanier said.
But fewer people won’t diminish the police presence. D.C. police — with about 3,900 officers — are deputizing more than 2,000 from 40 states to help with security, comparable with 20‘09.
Lanier said the extra help will ensure that the department doesn’t have to pull officers from neighborhood patrol shifts to staff the inauguration. Most of the officers from outside agencies will line the parade route
The National Guard is deploying more than 6,000 soldiers and airmen. Another 2,000 will be stationed just outside the city.
They will come from more than 25 states and territories, including Alabama, California, New York, Puerto Rico, and the US Virgin Islands.