WASHINGTON —For all the Obama administration’s vocal concern about Islamist extremists fighting in Syria, neither U.S. officials nor regional allies have taken significant action to stem the flow of jihadists to rebel ranks.

The jihadist pipelines _ mainly via Turkey, but also through Jordan and Iraq _ are an open secret, according to interviews this month with fighters and eyewitnesses, as well as analysts who’ve closely monitored the 2-year-old uprising against President Bashar Assad’s regime.

The foreign fighters would be hard to miss for Turkish and Western intelligence operatives _ they stay at established safe houses, openly recruit comrades and often stand out with distinctive appearances and habits _ yet there’s been no overt effort to crack down on their presence in frontier towns.

“Even with this growing jihadist threat, there’s a reluctance to do anything more proactive on Syria,” said Elizabeth O’Bagy, an analyst with the Institute for the Study of War who recently spent two weeks traveling with rebels in Syria, where she encountered Tunisian, Moroccan and Algerian fighters, she said. That observation was similar to what a McClatchy Newspapers reporter witnessed during a recent trip to Syria, where he saw Egyptians and Libyans, as well as other nationalities, among rebel fighters.

“The pipelines are still open and fighters are coming in quite freely,” O’Bagy said.

Such a laissez-faire approach not only runs counter to the alarmist public comments from the State Department on extremist elements trying to “hijack” the Syrian rebellion but it’s also a marked change from the way the government dealt with the jihadist “rat lines” that once ran in the opposite direction _ out of Syria into neighboring Iraq to fight U.S. forces before the American military withdrew at the end of 2011.

During the Iraq War, the U.S. government spent millions of dollars helping the Iraqis beef up border security and intercept the fighters and weapons that were streaming into the country.

By contrast, McClatchy couldn’t find a single public mention of authorities arresting a suspected jihadist at the Turkish border or any signs that the U.S. was pressuring Turkey to be more vigilant at crossings such as Bab al-Hawa, the Syrian town across the border from Reyhanli, Turkey, that’s firmly under rebel control.

“Essentially, Turkey is running a rat line of jihadists into Syria the same way the Syrians ran a rat line into Iraq,” said Joshua Landis, the director of the Center for Middle East Studies at the University of Oklahoma and author of the blog Syria Comment. “Turkey, with America’s blessing, is doing the same thing and we’ve done nothing to stop them. It’s a wink nod-nod situation.”

State Department officials reject the idea that they’ve turned a blind eye to the traffic, but they wouldn’t go into detail on any possible discussions with Syria’s neighbors about hardening the borders and better tracking foreign fighters.

“In our continuing discussions with our partners in the region, we are emphasizing the need for all countries that border Syria to take steps to prevent extremist elements like Jabhat al-Nusra from entering Syria,” a State Department official said, referring to an anti-Assad group, known as the Nusra Front in English, that the United States has said is an incarnation of the group al-Qaida in Iraq. The diplomat, who wasn’t authorized to discuss the matter publicly, spoke only on the condition of anonymity.

Analysts offer mixed views on why the U.S. hasn’t done more to block the jihadist routes. They argue that the pipelines are less of a priority for the administration because the jihadists aren’t targeting Americans _ as they were in Iraq _ that U.S. diplomats want to avoid confronting the Turks on the issue because they need Turkey’s help on other urgent regional matters and, perhaps most importantly, that the battle-skilled jihadists are a necessary evil to hasten the U.S. goal of ousting Assad.

“It’s kind of like Lincoln talking about Grant: I don’t care if he’s a drinker, he fights,” said a former senior U.S. government official with extensive experience in the Middle East, who spoke on the condition of anonymity because of the political sensitivity of the Syrian crisis.

Plus, analysts agreed, the Obama administration simply was slow in general to acknowledge the extremist infiltration of the Syrian uprising, which Washington sought to portray as nonviolent and pro-democracy long after evidence emerged of armed attacks on pro-regime forces and a growing presence of Syrian and foreign fighters whose stated goal was to replace Assad’s dictatorship with ultraconservative Islamist rule.

“For a long time there was undue optimism that the rebellion in Syria would result in a progressive, democratic-leaning movement. Frankly, they didn’t see the jihadi movement,” said Brian Fishman, a counterterrorism expert at the Washington-based New America Foundation, a public policy institute based in Washington, who conducted extensive research on the jihadist pipelines of the Iraq War.

“There was a willful ignorance of reality there because we wanted Syria to be simpler than it is,” Fishman added. “The reality is that the situation in Syria raises tremendous policy questions and moral questions.”

Jihadist media outlets advertise locations in Turkey or just inside Syria where volunteer fighters may connect with handlers who offer shelter and match them with fighting groups, including the Nusra Front. Foreign fighters slip easily across the border, often without so much as having their passports examined.

While some join the more moderate or secular rebel brigades, many seek to connect with Nusra or an allied group, Ahrar al-Sham.

A 37-year-old Egyptian father of two who goes by the nom de guerre Abu Rami said he’d crossed into Syria four times in the past year, mostly to fight but also to offer lessons on Islamic law, which he’s formally studied.

Abu Rami said he’d never had to sneak in and had never experienced any hindrance from Egyptian or Turkish authorities. He easily obtains a Turkish visa in Egypt and then makes his way to the Bab al-Hawa crossing, where he links up with a Syrian comrade who guides him to a rebel unit. The whole trip, he said, costs no more than 1,500 Egyptian pounds, roughly $220.

“The majority of Egyptian jihadists in Syria aren’t affiliated with political parties or the Islamist movement in Egypt,” Abu Rami said. “They’re mostly independent, well-educated people with no financial or social problems, and come from good families. But their motivation is based on true jihad that knows no borders.”

Another Egyptian fighter, a British-educated father who goes by the pseudonym Abu Ahmed, said he’d chatted with Syrian rebels for months via the video teleconferencing service Skype before deciding he was ready for battle in January. He, too, entered without incident via Bab al-Hawa.

The Syrian rebels, he said, sold him a Kalashnikov for $700 and taught him how to use it.

• Hannah Allam and David Enders, Associated Press