WASHINGTON – Infants have been stopped from boarding planes at airports throughout America because their names are the same as or similar to those of possible terrorists on the government’s “no-fly list.”

It sounds like a joke, but it’s not funny to parents who miss flights while scrambling to have babies’ passports and other documents faxed.

Ingrid Sanden’s 1-year-old daughter was stopped in Phoenix before boarding a flight home to Washington at Thanksgiving. “I completely understand the war on terrorism, and I completely understand people wanting to be safe when they fly,” Ms. Sanden said. “But focusing the target a little bit is probably a better use of resources.”

The government’s lists of people who are either barred from flying or require extra scrutiny before being allowed to board airplanes grew markedly since the September 11, 2001, attacks. Critics including the American Civil Liberties Union say the government doesn’t provide enough information about the people on the lists, so innocent passengers can be caught up in the security sweep if they happen to have the same name as someone on the lists.

That can happen even if the person happens to be an infant like Ms. Sanden’s daughter. (Children under 2 don’t need tickets but Ms. Sanden purchased one for her daughter to ensure she had a seat.)

“It was bizarre,” Ms. Sanden said. “I was hugely pregnant, and I was like, ‘We look really threatening.'”

Sarah Zapolsky and her husband had a similar experience last month while departing from Dulles International Airport outside Washington.

An airline ticket agent told them their 11-month-old son was on the government list.

They were able to board their flight after ticket agents took a half-hour to fax her son’s passport and fill out paperwork. “I understand that security is important,” Ms. Zapolsky said. “But if they’re just guessing, and we have to give up our passport to prove that our 11-month-old is not a terrorist, it’s a waste of their time.”

Ms. Sanden and Ms. Zapolsky would not allow their children’s names to be used in this story because they fear people who prey on children.

Well-known people like Senator Kennedy; Rep. John Lewis, a Democrat of Georgia, and David Nelson, who starred in the sitcom “The Adventures of Ozzie and Harriet,” also have been stopped at airports because their names match those on the lists.

The government has sought to improve its process for checking passengers since the September 11, 2001, attacks. The first attempt was scuttled because of fears the government would have access to too much personal information. A new version, called Secure Flight, is being crafted.

But for now, airlines still have the duty to check passengers’ names against those supplied by the government. That job has become more difficult – since the 2001 attacks the lists have swelled from a dozen or so names to more than 100,000 names, according to people in the aviation industry who are familiar with the issue. They asked not to be identified by name because the exact number is restricted information.

Not all those names are accompanied by biographical information that can more closely identify the suspected terrorists. That can create problems for people who reserve flights under such names as “T Kennedy.”

ACLU lawyer Timothy Sparapani said the problem of babies stopped by the no-fly list illustrates some of the reasons the lists don’t work.

“There’s no oversight over the names,” Mr. Sparapani said. “We know names are added hastily, and when you have a name-based system you don’t focus on solid intelligence leads. You focus on names that are similar to those that might be suspicious.”

The Transportation Security Administration, which administers the lists, instructs airlines not to deny boarding to children under 12 – or select them for extra security checks – even if their names match those on a list.

But it happens anyway. Deborah McElroy, president of the Regional Airline Association, said: “Our information indicates it happens at every major airport.”

The TSA has a “passenger ombudsman” who investigates claims from passengers who say they are mistakenly on the lists. TSA spokeswoman Yolanda Clark said 89 children have submitted their names to the ombudsman. Of those, 14 are under the age of 2.

If the ombudsman determines an individual should not be stopped, additional information on that person is included on the list so he or she is not stopped the next time they fly.

Ms. Clark said even with the problems the lists are essential to keeping airline passengers safe.