She also reiterated a warning against any attempt by the Syrian government to use its chemical weapons stockpile against the rebels, calling this a "red line" that would prompt US action.
The 28 NATO allies meet in Brussels on Tuesday and Wednesday. Turkish Foreign Minister Ahmet Davutoğlu will be attending the talks, the Foreign Ministry confirmed on Monday.
Turkey, which has made a formal request to NATO to help it bolster its air defenses, is a big supporter of opposition forces fighting to oust Syria's President Bashar al-Assad. It has repeatedly scrambled jets along the countries' joint border and responded in kind when shells from the conflict have landed inside Turkey, underlining fears Syria's 20-month-old revolt could spread to destabilize the region.
"We're all positively considering [the request]," a senior State Department official said, briefing reporters en route to Europe, where Clinton started a regional trip with a stop in Prague. "[We] are hopeful that NATO will be in a position to respond positively ... and that the three contributing countries that are being considered -- the United States, Germany and the Netherlands -- will be in a position to also contribute."
The official said he did not expect final details this week on the numbers of missiles that would be deployed, or on where or for how long, as site surveys were still going on. He also said it would also probably be "at least a matter of weeks" before deployment, as national decisions still had to be made and site surveys completed and agreed.
A NATO delegation surveying sites for possible deployment of Patriots has concluded its trips to Adana, which hosts a US air base, and Hatay on the border with Syria, the Anatolia news agency reported on Monday. The NATO team will report back to NATO once its exploration is concluded. NATO commanders will then draw up a recommendation to alliance ambassadors on where the missiles should be deployed.
Russia, which will join the NATO meeting, has been at odds with the alliance over how to end the Syrian conflict. Russia has vetoed UN resolutions aimed at pressuring Assad to step down and Moscow's foreign minister, Sergey Lavrov, is expected to raise concerns over the missile deployment plans.
The State Department official said the deployment would not be part of "an inexorable move towards a no-fly zone" over Syria of the sort NATO mounted to defend anti-government rebels in Libya.
The official also rejected the idea that deployment of Patriots in Turkey would create a de-facto safe haven in Syria's border area with Turkey, as the missiles would be used to defend against planes or missiles that crossed into Turkish airspace. The possibility of establishing a no-fly zone is expected to be discussed at a meeting of the Friends of Syria group in Marrakech next week.
"We're always prepared -- and the secretary has made that clear -- to look at ways in which we can help the people of Syria," the official said. "But ... a no-fly zone is not on the agenda of any NATO talks this week."
Turkey has also insisted that the Patriot deployment is only for defense purposes. On Sunday, the Guardian quoted Turkish officials as saying that the Patriot request followed intelligence that the Syrian government was contemplating the use of missiles, possibly with chemical warheads.
The officials, speaking on condition of anonymity, told the British daily they had credible evidence that if the Syrian government's aerial bombardment against opposition-held areas failed to hold the rebels back, Bashar al-Assad's regime might resort to missiles and chemical weapons in a desperate last effort to survive.
Addressing a possible threat of chemical weapons from Syria, Clinton said, “We have made our views very clear: This is a red line for the United States.”
"I'm not going to telegraph in any specifics what we would do in the event of credible evidence that the Assad regime has resorted to using chemical weapons against their own people. But suffice it to say, we are certainly planning to take action if that eventuality were to occur,” she told a press conference during a visit to Prague.
Syria swiftly responded to Clinton's statement, saying such weapons will never be used against the Syrian people. "In response to the statements of the American secretary of state, who warned Syria against using chemical weapons, Syria has stressed repeatedly that it will not use these types of weapons, if they were available, under any circumstances against its people," a Syrian Foreign Ministry statement said.