* Worry about precedent for Jordan as US ally against Qaeda
* Jordan: release brokered with Libyan gov't, not kidnappers
By Suleiman Al-Khalidi
AMMAN, May 13 (Reuters) - Kidnappers freed Jordan's ambassador to Libya and he said on his arrival home on Tuesday that in exchange his government had sent back to Tripoli a Libyan Islamist militant who had been serving a life sentence for a bombing plot.
Jordan's foreign minister said the envoy's release was arranged in contacts with Libyan authorities, not with the kidnappers. But some Jordanian officials voiced concern at the precedent the handover of the militant could set for Amman, an important U.S. ally in the fight against al Qaeda.
A Libyan foreign ministry spokesman told al-Nabaa television channel that militant Mohammed Dersi was back in Libya. Asked repeatedly whether Dersi was in prison or free, he said only: "Dersi is in Libya and he is fine."
Jordanian Ambassador Fawaz al-Itan was kidnapped last month by Libyan gunmen who demanded an Islamist militant be freed from a Jordanian jail in exchange for the diplomat's release.
Fawaz al-Itan told well-wishers including Jordan's prime minister on arrival at Amman airport that he had been swapped for Dersi, who he said had been removed from a maximum-security Amman prison and flown to Libya.
"The swap was concluded in a very civilised way. I shook Dersi's hand and welcomed his release and arrival in Libya," said Itan, adding that he was treated well by his captors.
Dersi and several other Qaeda suspects were jailed for life in 2007 for plotting to blow up Amman airport.
Jordanian Foreign Minister Nasser Joudeh denied any swap had been negotiated with the kidnappers, saying Itan's release had was part of a legal arrangement struck with Libyan authorities.
"There was no exchange or swap or deal," he told reporters.
Judicial sources said Amman had been quietly working out a face-saving deal that initially aimed to return Dersi to Libya to serve the remainder of his sentence at home.
But the kidnappers insisted on Dersi's immediate release, leaving Jordanian authorities with little alternative, according to the sources. "Yes we saved the life of Itan but the political cost of succumbing to the demands of terrorists in future might be higher," said a Jordanian official who requested anonymity.
Analysts said that agreeing to the kidnappers' demand could set a risky precedent for the U.S.-aligned Arab kingdom, which has been at the forefront of covert operations against militant Islamists in the Middle East.
Some Jordanian officials privately expressed worry that the release of a jailed al Qaeda militant would raise the danger to Jordanian targets abroad by emboldening other militants.
The kingdom has some high-profile radical Islamists in its jails, including cleric Abu Qatada who was deported from Britain, and Mohammad Maqdisi, a fundamentalist theorist.
Kidnappings have become commonplace in widely lawless Libya, with foreign diplomats often the targets used to press for the release of Libyan militants jailed overseas. (Additional reporting by Ulf Laessing in Tripoli, Editing by Mark Heinrich)