UPDATE 4-Airplane bomb suspect said cooperating with U.S.

* US flies Abdulmutallab's family members from Nigeria

* US officials say he is giving them useful intelligence

* Blair says Qaeda sure to try attacking U.S. again soon (Blair says attempted Qaeda attack on U.S. soil within six months is certain, paragraphs 2, 20)

By Jeremy Pelofsky and Tabassum Zakaria

WASHINGTON, Feb 2 (Reuters) - The Nigerian man accused of trying to blow up a U.S. airliner on Christmas Day has provided "useful, actionable" intelligence to U.S. authorities after the FBI flew his relatives to the United States to urge him to cooperate, U.S. officials said on Tuesday.

And top U.S. intelligence officials, testifying on Capitol Hill about the attempted bombing and other security threats, said al Qaeda and its allies were "certain" to try to attack U.S. territory again within the next six months.

The bombing suspect, Umar Farouk Abdulmutallab, 23, started talking again after FBI agents brought family members from Nigeria to help convince him to provide information on how the botched Dec. 25 bomb plot was arranged and whether further attacks were in the works, a senior U.S. official said, speaking on condition of anonymity.

He is alleged to have mounted the attack with help from a Yemen-based al Qaeda branch.

"I'm confident he's going to continue to cooperate," the official said, although he declined to say whether Abdulmutallab had been offered a plea deal or leniency in exchange for answering questions again.

The Obama administration has been criticized by Republicans and Democrats because Abdulmutallab was interviewed by FBI agents for about an hour before he stopped cooperating and he was then read his so-called Miranda rights, providing him full U.S. constitutional legal protections.

They questioned if that prevented getting intelligence.

Prosecutors charged Abdulmutallab with trying to blow up the flight from Amsterdam to Detroit with a bomb sewn into his underwear, drawing further criticism from some lawmakers who said he should face a special military tribunal instead and questioning by intelligence operatives instead of the FBI.

"Abdulmutallab is talking and has been talking since last week providing useful, actionable and current intelligence that we've been actively following up on," a U.S. law enforcement official said, declining to be named because the investigation is ongoing.

If convicted, Abdulmutallab could spend the rest of his life in prison, a fate that may provide an incentive for him to cooperate with FBI investigators interrogating him with support from CIA agents.

'FULLY APPRISED'

President Barack Obama was kept "fully apprised" on Abdulmutallab's change of heart, the senior U.S. official said. Obama, who has ordered reforms to prevent future security lapses such as those that occurred in this incident, had faced criticism from Republicans for waiting three days during a Hawaii vacation to comment on the attempted bombing.

In the days following the attempted bombing, two FBI agents flew to Nigeria and gained help from Abdulmutallab's family members who then proved "instrumental" in winning his cooperation, the senior administration official said.

He declined to say whether Abdulmutallab's father, who warned U.S. officials in Lagos before the failed attack that his son had been radicalized, was among the relatives who agreed to fly to the United States on Jan. 17.

Senator Christopher Bond, the top Republican on the Senate Intelligence Committee, argued that giving Abdulmutallab legal rights still gave anti-American militants time to cover their tracks. "We will never know what life saving information on co-conspirators and future plots we missed out on," he said.

Director of National Intelligence Dennis Blair told lawmakers there should be flexibility to make decisions on a case-by-case basis about whether such suspects go through a civilian or military legal process.

Before Abdulmutallab stopped talking, administration officials have said he initially provided useful information.

That included telling investigators that he had received training as well as the explosive device from militants in Yemen affiliated with al Qaeda.

The Yemen-based al Qaeda group has become a significant concern to U.S. intelligence agencies that are monitoring its capabilities, intentions and recruitment of Westerners, Blair told the Senate Intelligence Committee.

Blair also said he believed gaps had been fixed since the Dec. 25 incident.

"I'm confident that someone who left the trail that Mr. Abdulmutallab did would now be found," Blair said. "What I can't tell is even with these improvements we would be able to catch someone who took more care."

Asked about the likelihood of an attempted attack by al Qaeda on U.S. soil in the next three to six months, Blair said an attempt was "certain." Other intelligence officials agreed.

In an audiotape aired recently on Al Jazeera television, a man purporting to be al Qaeda leader Osama bin Laden praised Abdulmutallab and vowed more strikes at the United States. (Additional reporting by Matt Spetalnick; Editing by Will Dunham, Chris Wilson and Paul Simao)