Dozens of reporters showed up to a pen-and-pad briefing on inaugural security Thursday afternoon, but officials mostly stuck to one theme: We don’t know yet.

“We do not have the entire picture today,” said Malcolm Wiley, spokesman for the Secret Service. “There have been some recent developments that have changed the scope of what we’re doing.”

One of those developments is the expectation that more than a million people will show up for President-elect Barack Obama’s inauguration, flooding streets, Metro cars and buses.

But officials were vague on how this year’s security plans will differ from past inaugurations.

Certainly, there will be more officers on the street. The Metropolitan Police Department alone is bringing 8,000, half of which will come from law enforcement agencies across the country. That’s 1,000 more officers than at President George W. Bush’s inauguration in 2005.

However, officials declined to estimate the number of officers from other agencies, such as the Secret Service, the FBI and the military. And although they said everyone should expect to be screened — on the Mall, along the parade route and outside the Capitol — they said they hadn’t yet finalized those plans.

Among other plans agencies are still working on: evacuations, street closures and a public announcement system. The D.C. Department of Transportation has identified about two-thirds of the parking spaces they will need for an expected 10,000 buses — 9,000 more than during the height of the Cherry Blossom Festival.

Officials did have some advice, however: Spectators should bring as little as possible, though chairs and coolers will technically be allowed on the Mall (but not on the parade route or in the inauguration’s ticketed area). Don’t show up on the Mall in the middle of the night. Instead, wait until the Metro opens at 4 a.m.

And whenever possible, walk. A spokeswoman for the Metro Transit Authority painted a grim picture of public transportation, emphasizing that Metro officials expect a “crush load” and will not be able to handle more than 120,000 trips an hour.

As a National Special Security Event, the inauguration is headed by the Secret Service, with the help of 60 other local and federal agencies. Twenty-three subcommittees plan for everything from explosions to public affairs.

For the official inauguration ceremony, about 1,600 Capitol Police will join an untold number of Secret Service agents in securing a perimeter around the Capitol. Security for that ticketed area — for which about 240,000 tickets will be distributed — was not discussed in depth on Thursday.