By Yara Bayoumy and John Walcott

WASHINGTON (Reuters) - U.S. Secretary of State John Kerry heads to Moscow on Thursday to again seek deeper Russian cooperation in the war against Islamic State in Syria, but he faces strong opposition from defense and intelligence officials who argue that Washington and Moscow have diametrically opposite objectives in the country.

Kerry's trip, which State Department officials say is his second to the Russian capital this year and his third in 12 months, takes place as U.S.-Russian relations have worsened with tit-for-tat diplomatic expulsions, aggressive Russian maneuvers toward U.S. aircraft and vessels, and a disregard for a cessation of hostilities in Syria, where Russia has bombed U.S.-backed rebels.

Relations between Moscow and Washington also remain strained over the Ukraine crisis and what the Kremlin considers NATO’s unjustified activities along its borders, raising fears that disagreements could escalate into confrontations, either accidental in Syria or the result of miscalculations in the air and naval encounters from the Baltics to the Black Sea.

Yet Kerry, it seems, still hopes for closer collaboration with Russia, to the disbelief of many officials who say Washington has no strategy on how to deal with the challenges Russia poses in Europe and Syria.

"It isn't clear why the secretary of state thinks he can enlist the Russians to support the administration's goals in Syria," said one U.S. intelligence official.

"He's ignoring the fact that the Russians and their Syrian allies have made no distinction between bombing ISIS and killing members of the moderate opposition, including some people that we’ve trained," the official said, using an acronym for the militant group. "Why would we share intelligence and targeting information with people who’ve been doing that?" ANGRY SPIES

Many U.S. intelligence officers are incensed by the administration's continued overtures to Russia, in part because they say the Russians knew a rebel camp they bombed twice housed families of U.S.-backed rebels whose only mission is to pursue Islamic State.

The first attack on the camp killed at least 123 people and injured scores more, said two U.S. intelligence officials. The second, on Tuesday, killed at least 12 more, they said.

The camp, the officials said, is in a no-man’s-land on Syria’s border with Jordan devoid of any Syrian troops or Islamic State fighters, and the Russians attacked it deliberately, the officials said.

Other officials argue it is naïve to think that because the Russians say they, too, are seeking a negotiated end to Syria’s civil war - which, according to the United Nations, has claimed some 400,000 lives - Moscow’s goal is compatible with that of the United States and its Arab and European allies.

"The Russians want a settlement that would keep (Syrian President Bashar al-)Assad or some replacement acceptable to them in power," said a defense official, who like others who discussed the schism in the administration agreed to do so only on condition of anonymity.

"The president has said that Assad has got to go, and our allies, especially the Saudis, hold that view very strongly. In fact, they keep asking us why we’re cozying up to Moscow." "ANOTHER GO"

State Department spokesman Mark Toner said Kerry was going to Russia "yet again" to have "another go" at getting Moscow to buy in to a process that could lead to a nationwide cessation of hostilities.

"There are areas with regard to Syria and how to resolve the conflict on which we agree," he said. However, he added: “While we have reached those overarching agreements, we have not seen the practical reality on the ground yet.”

But even some of Kerry’s own State Department subordinates question why their boss is trying to move forward, meeting on Thursday with Russian President Vladimir Putin and on Friday with Foreign Minister Sergei Lavrov – in Moscow, no less, said one – when U.S.-Russian relations are slipping backward.

The latest evidence of that came on Wednesday, when Russia refused to let Jeff Shell, chairman of the U.S. Broadcasting Board of Governors, which oversees Radio Free Europe and other government-backed news outlets, enter the country.

A board statement said Shell was denied entry and detained in a locked room at Moscow's Sheremetevo Airport for several hours on Tuesday despite having a valid passport and Russian visa.

Accompanied by Russian security officials, he later boarded a flight to Amsterdam and was told he was subject to a "lifetime ban" from Russia.

The Russian Foreign Ministry said Shell had been on a 'stop list' for a long time, adding that he was "one of the organizers of lying anti-Russian propaganda, financed from the American budget, that is implementing the political decisions taken at the very top of the U.S."

His treatment is consistent with his name being on a blacklist of individuals Russia has decided to block, though Moscow has shrugged off accusations that U.S. officials in Russia were facing increased harassment.

Last month, Washington expelled two Russian officials in response to what it described as a Russian policeman's attack on a U.S. diplomat in Moscow earlier that month.

A spokesman for the U.S. Embassy in Moscow did not have immediate comment.

"I think quite frankly (Kerry's) visit is a microcosm of the confusion about U.S. policy towards Russia," said Heather Conley, director of the Europe Program at the Center for Strategic and International Studies think tank in Washington.

"It's a lot of political capital to send the secretary of state if you don't have a clear objective of what you want to accomplish," she told Reuters.

(Additional reporting by Lesley Wroughton and Jonathan Landay in Washington and Andrew Osborn and Jason Bush in Moscow; Editing by Jonathan Oatis)