In its bid to push more people to use SmarTrip cards, Metro has been offering a $3 rebate to anyone who buys one.

But since Metro started the incentive in September, most riders who have purchased new cards haven’t claimed their rebates.

While the transit agency sold nearly 352,000 SmarTrip cards during the last four months of 2012, just 67,112 rebates had been issued as of Jan. 4.

It’s not clear why four out of five riders who bought new cards are forgoing the rebates, though in the retail world, consumers regularly fail to redeem rebates.

“Companies that feature rebates know that a certain proportion of them won’t be claimed,” said Linda Sherry, the Washington director of Consumer Action, a consumer advocacy and education nonprofit group based in San Francisco. “In general, people think of rebates as kind of a hassle.”

One explanation for the unclaimed rebates, according to Metro spokesman Dan Stessel, could be that most regular riders already have cards. Many of the more recent purchases may have been by people who rarely use the system or who were visiting.

Another possibility is that many riders focused on the fare increases that arrived last year and forgot about the rebate. “I think it’s because people were so outraged by the fare hikes . . . people in general just didn’t pay attention to that rebate,” said James Wright, a member of Metro’s Riders’ Advisory Council from Prince George’s County.

And the rebate isn’t big enough to make people notice, Wright said. A $3 rebate wouldn’t even be enough to get a rider from Metro Center to New Carrollton during the evening commute, he said. “If you set up a program where I could get a $20 rebate, I would definitely sign up for it and do what I needed to do to get it,” he said. “But $3? Come on.”

To some travelers, though, even a $3 rebate has its virtues.

Brittany Kalkstein, a commercial real estate broker, lost her SmarTrip card last month and has been relying on paper farecards. When she buys a new card, she plans to register it and claim the rebate.

“It’s one Metro ride, that’s how I look at it,” said Kalkstein, 24.

To obtain the rebate, the card has to be registered online. Then a $3 rebate is sent to the card five days after it is first used.

Most people probably “just didn’t know about it,” Patricia Murphy, 53, of Southeast Washington said after buying a new card at Metro Center on Thursday. She only learned of the rebate from a reporter who asked her about it.

There is some fine print. The rebate has to be claimed within 30 days of being issued. It cannot be issued if the card has a negative balance.

And it has to be claimed at a station that riders have used during the previous 20 days. So if a commuter traveled through Union Station over Thanksgiving and hasn’t been back since, he or she can’t go there in January to claim the rebate. Riders in that situation have to return to a station they have used during the 20-day window.

The process is slightly different for Metrobus riders; as long as a traveler has used Metrobus in the 20 days before grabbing the rebate, the person can claim it on any other Metrobus.

The rebate was part of Metro’s push to get riders to stop using paper farecards. As part of the systemwide fare increases that arrived this past July, a $1 surcharge was added to every trip taken with a paper farecard.

Metro began offering the rebate in September because cheaper chips in the cards lowered the actual cost of the card, to $2 apiece. The rebate was supposed to coincide with SmarTrip vending machines arriving in every station, but many of these machines became operational only months later because Metro didn’t ensure that they complied with the Americans With Disabilities Act. It wasn’t until November that every station finally had machines dispensing the cards.

Wright questioned why the rebate was necessary at all. “Just take away the rebate and sell it at a cheaper price,” he said.

But Stessel said they can’t sell the cards for $2 because the potential for fraud would be too high. SmarTrip cards can have negative balances, and riders need just $1.20 on their cards to enter the system. Someone could buy a card for $2, take a trip from Glenmont to Vienna costing $5.75 and throw away the card.