Wal-Mart and Best Buy are stocked with $50 digital-converter boxes for last-minute procrastinators, and the government says it will have 4,000 phone agents available tomorrow to answer urgent calls about lost TV reception.

That's because the nation's local TV broadcasters, in a staggered fashion throughout the day, will extinguish the age-old analog TV signals for new digital ones that improve picture quality and make available more free-TV channels. Digital TV transmissions also could lead to mobile-TV devices, industry experts say.

Digital TV signals can be received by older TVs with the help of a government-subsidized digital-converter box. Depending on tree foliage and the topography around the home, a person might need a new antenna, too.

"People are very confused, and who knows what will happen," said Joe Fuhr, an economics professor at Widener University who has studied the transition. "People with the most problems are the elderly and those who don't speak English."

The Obama administration and Congress delayed the over-the-air digital-TV transition for four months this year so people could prepare.

People are supposed to buy a digital-converter box or a new digital TV, or switch to cable or satellite, to prepare for the conversion.

Government and industry officials estimated today that about 3 million free-TV households used the delay to get ready.

Still, 2.2 million to 2.8 million households could lose reception, various industry and government sources say. There are a total of 12 million to 15 million free-TV households in the United States.

About 145,000 households get only free over-the-air TV in the Philadelphia region, which includes Wilmington, Allentown, and Atlantic City, according to estimates by the Nielsen Co.

Fifty-five thousand households in the Philadelphia area are unprepared for the conversion, Nielsen estimates. There are about 2.95 million TV households in the region, which means that over-the-air TV households are about 5 percent of the TV market.

Mary Bumpas, 72, of Germantown, said today that her TV was saying "bad signal" or "no signal." She had not worked out the kinks in the converter box for two months. "I'll have to wait and see what happens tomorrow," she said hopefully.

U.S. taxpayers subsidized the TV transition with $2.3 billion, mostly for $40 coupons for the digital-converter boxes. Each household is eligible for two. At this point, it will take about 10 days for a person to get a coupon. A person can order converter coupons through www.dtv2009.gov or by calling 1-888-388-2009 through July 31, or until supplies run out.

Broadcast and government officials were cautiously optimistic today in a Washington news conference. But they were expecting some problems. "All of us recognize that this will not go perfectly well," said Kyle McSlarrow, the president of the National Cable & Telecommunications Association.

"I'm sure there will be surprises," said Ellen Goodman, a law professor at Rutgers-Camden who was a lawyer in Washington representing broadcast companies.

The Federal Communications Commission said it had planned for calls from people who lost over-the-air TV reception, staffing centers with 4,000 agents. They can be reached at 1-888-225-5322 (CALL-FCC).

Congress, through an economic-stimulus bill passed earlier this year, has funded free in-home digital-converter box installers and walk-in information centers.

There are walk-in centers available around the region. One is in The Gallery in Center City and another in Cheltenham Mall, according to the FCC Web site. A woman who answered the phone listed on the FCC Web site said the mall facilities were kiosks.

Pay-TV providers, such as Comcast Corp. and DirecTV, could gain subscribers because people are confused about digital or cannot receive the new digital signal.

Contact staff writer Bob Fernandez at 215-854-5897 or bob.fernandez@phillynews.com.