Temporary cell phone towers are being installed on the National Mall for the presidential inaugural. (Michael S. Williamson/The Washington Post)

President Obama’s second inauguration may bring smaller crowds to the Mall than his first, but officials worry that potent new wireless gadgets will clog the airwaves above the festivities just as before.

Wireless traffic congestion was a big problem four years ago, when 1.8 million people packed the Mall for the inauguration and called the folks back home with what are now antiquated cellphones.

Less than half that many people are expected this time, but they will be armed with much more powerful smartphones and tablets, some of which require more than 120 times the bandwidth of a basic cellphone.

So phone companies are setting up an extensive network of temporary towers and other equipment the length of the Mall to handle the explosion in wireless traffic.

“Last time around, the sheer number of people . . . overloaded the system and many cellphones in the crowd just couldn’t get a signal,” Sen. Charles E. Schumer (D-N.Y.), chairman of the Joint Congressional Committee on Inaugural Ceremonies, said in a statement.

“We don’t want that to happen again,” he said. “The inauguration is a once-in-a-lifetime experience . . . so we’re putting measures in place to make sure people can call, tweet, Facebook and document their experience on smartphones and social media.”

So far, at least nine temporary cell towers — including COWS, or cells on wheels — have gone up near the Korean War memorial, the World War II memorial, the Washington Monument, the National Gallery of Art, two Smithsonian museums and other locations.

The increased infrastructure is “for all the people that are going to be on the national Mall on the given day of the inauguration . . . and the parade,” Sprint Nextel spokeswoman Crystal N. Davis said.

“They’ll be using their cellphones. They’ll be tweeting. They’ll be sending pictures,” she said. “They’ll be doing all manner of things with their cellphones that they probably weren’t able to do” four years ago.

She said the company has stationed three COWS as well as a SatCOLT (satellite cell on light truck) around the Mall — the latter to help with communications by emergency crews. Four years ago, it had one COW and one SatCOLT.

It has also installed signal repeaters in three hotels — the Mayflower, the Marriott Wardman Park and the Capital Hilton — to enhance service there.

The president is scheduled by law to be sworn in Jan. 20, a Sunday, but a ceremonial inauguration and parade are set for Jan. 21. Several hundred thousand people are expected to attend, many with the latest wireless devices.

“As people buy tablets and smartphones . . . it really puts . . . demands on the network,” said Brian Josef, assistant vice president of regulatory affairs for CTIA — the Wireless Association, an industry trade group.

Such devices use far more bandwidth than the basic cellphone, he said.

The inaugural activities pose “a unique situation where a tremendous number of people [are] using large amounts of bandwidth on the network in a confined area,” he said. “It’s not without challenge.”

The inauguration is the largest regular public gathering in the area, said Lawrence McWright, who oversees the mobility network for AT&T in Washington and Baltimore. He said he and his team have been planning for the past 18 months.

He said AT&T’s wireless capability around the Mall is like “night and day” compared with four years ago. In 2009, “you had people making phone calls, using text and doing a small amount of data,” he said.

“Today, people are doing all kinds of stuff on their mobile phones and tablets and other connection devices: video, social media, sharing things on Facebook,” he said. “It’s changed so much in a short time frame.”

He said a smartphone uses 35 times the bandwidth of a basic cellphone, and a tablet uses 121 times the bandwidth.

He said AT&T had only “a couple” of temporary towers on the Mall in 2009. This year “AT&T will have nine the length of the Mall,” he said. “We’ll have some other temporary sites along the parade route.”

Of the nine that were spotted last week, he said, some are AT&T’s, and some belong to other companies.

“We’ve increased capacity 200 percent [from what’s normally there] to help with the volume that we expect,” he said. The company has also boosted capacity at nine hotels and the two major airports in Northern Virginia.

T-Mobile and Verizon Wireless said they, too, have added capacity around the Mall

But even with the increases, the companies said, there could be delays and glitches.

“Even with . . . these temporary towers,” said Josef, “you can see some delays, some congestion on the network.”

“We’re kind of the victims of our own success,” he said.

McWright, of AT&T, urged people to text whenever they can, “save then send,” or use WiFi hotspots. Sending video uses the most bandwidth, he said, and texting and tweeting take the least.