Admirers of Bill McRaven like to tell a story of his courage and grit. Not against the enemy, but against the legendarily ruthless Dick Marcinko, a gung-ho Navy SEAL commander in the Vietnam era who used to swallow sacs of cobra venom and boast that "killing is my mission." Marcinko once ordered McRaven, then a young lieutenant on the super-elite SEAL Team Six, to perform "some questionable activities," recounts a former Special Forces commander. McRaven refused and "would not back down." (Marcinko did not return phone calls seeking comment.) "McRaven was a hero among all the junior officers for his stand," says the commander. "It was considered a career-ending move."

Not quite. William H. McRaven, it seems, was too good an officer. Today he is a rear admiral, and his new job is one that could not rank higher on President George W. Bush's to-do list in election year 2004: nailing Osama bin Laden. It is a job that will require much ruthlessness--a good deal more of that, perhaps, than personal honor. NEWSWEEK has learned that McRaven is heading up Task Force 121, a covert, miniature strike force with a command structure so secretive that McRaven's role hasn't even been reported until now.

Task Force 121, which also helped to capture Saddam Hussein under McRaven's command, represents something brand-new in warfare, a pure hybrid of civilian intelligence and military striking power. It is the most ambitious melding yet of CIA assets, Special Forces (mainly the Army's Delta Force) and the Air Force. Formed late last year as part of Joint Special Operations Command--the secret "black ops" under Maj. Gen. Stanley McChrystal, who until recently was deputy operations director of the Joint Chiefs of Staff--it is designed to produce a lightning-fast reaction should intel locate bin Laden or any other "high-value targets" anywhere for a few hours. It's a work in progress: CIA Director George Tenet meets frequently with Gen. John Abizaid, the head of Central Command, to nurture the marriage.

McRaven has managed to bridge both the civilian and military worlds. While working at the National Security Council after 9/11, he was principal author of the White House strategy for combating terrorism. McRaven also literally wrote the book on Special Ops, a 1995 history of surgical strike teams from the Nazi rescue of Mussolini in 1943 to the 1976 Israeli raid on Entebbe. And his thesis at naval postgrad school is now mandatory reading for Special Ops commanders. "Bill is reputed to be the smartest SEAL that ever lived," says a former commander who knows McRaven well. "He is physically tough, compassionate and can drive a knife through your ribs in a nanosecond." According to his former boss at the White House, Gen. Wayne Downing, "if anybody is smart and cunning enough to get [bin Laden], McRaven and the Delta and SEAL Team Six guys he now commands will do it."

Is anybody good enough? The hunt for bin Laden is an unprecedented confrontation between 21st-century technology and age-old guerrilla tactics. While the elusive terror chieftain hides in mountain caves and scurries along mule trails, Task Force 121 "bytes" away at him and his chief deputy, Ayman Al-Zawahiri, with the best the Information Age has to offer. Using powerful software called Analyst's Notebook, which helps to piece together data on criminal and terror networks--Special Forces command just ordered up more copies--military and intelligence officials are increasingly confident they are narrowing bin Laden's whereabouts.

It's a classic cat-and-mouse game in which tactics abruptly shift on both sides. In years past, U.S. officials listened in on bin Laden's cell-phone conversations. But he apparently no longer dares to use electronic means of communication. So McRaven and his hunters are now trying to snare his couriers in transit. They scored a major victory two months ago with the capture of Hassan Ghul, a Qaeda operative who was carrying what U.S. officials say was a strategic memo from Abu Mussab al-Zarqawi, the mysterious terror leader allegedly behind the bombings of Shiites in Iraq. Ghul also yielded intel on bin Laden's position. Key to the search is "accumulated humint," or human intelligence, says one insider. Other officials tell NEWSWEEK that an increasing number of "data points"--reports of sightings--have created an ever-clearer picture of bin Laden's area of operation as he appears to shuttle between Pakistan and Afghanistan. Now they've focused that picture to the point where they have been able to send in Predator unmanned aerial vehicles to search for him.

If the hunters are getting closer to their prey, it's also thanks to a renewed effort by Pakistani President Pervez Musharraf to infiltrate the border regions sympathetic to Al Qaeda. On Saturday, the BBC reported that bin Laden narrowly escaped one such Pakistani raid, and NEWSWEEK confirmed that such an incident occurred. Within the past few weeks, some intelligence sources say, a U.S. Predator also spotted a suspect believed to be Al-Zawahiri somewhere in the border area.

Some Afghan and Pakistani sources, however, insist that bin Laden is several steps ahead--and that he will continue to outsmart his pursuers. A Taliban official in Pakistan, contacted by NEWSWEEK, says he's heard that both top Qaeda leaders moved to more secure and separate locations in January, before the spate of publicity about an American "spring offensive." The Taliban official learned that, he said, from a ranking Qaeda operative, a Yemeni who told him that other Qaeda and Taliban fighters had moved into Afghan provinces more than 100 miles from the Pakistani border. "We decided to leave the dangerous zone for safer areas," the Arab told the Taliban official, who goes by the nom de guerre Zabihullah. "The sheik is now in the most secure area he has ever been in," the Arab said, referring to bin Laden. "We were all laughing at all these recent reports that the Americans had our sheik cornered."

Zabihullah also said he received an encrypted e-mail last Thursday from a senior Qaeda source in Saudi Arabia. The Qaeda operative told him not to be taken in by the American "psychological warfare" campaign about bin Laden's imminent capture. He assured Zabihullah in the e-mail that "the sheik is in a safer place than ever and is more healthy than he's ever been."

McRaven could be using psyop to flush bin Laden and others out of their hiding places. But the real key to success, the Task Force 121 commander knows, may be the "hammer and anvil" of converging U.S. Special Forces teams in Afghanistan and some 70,000 Pakistani forces in the border areas. In one recent operation in Waziristan, Pakistani security forces arrested several women married to foreign fighters, hoping for a lead on bin Laden. Similarly, they have destroyed the houses of tribesmen suspected of sheltering Qaeda fugitives. Pakistani officials said the tactic has worked, providing valuable information while apparently helping to drive Qaeda and Taliban fighters back across the Afghan border--into the hands, they hope, of Task Force 121. The standing U.S. offer of $25 million for bin Laden's head provides an extra incentive. "We now have all the ingredients in place for more effective operations in the days to come," says a senior Pakistani official. The man who's been tasked with blending those ingredients together, Bill McRaven, is betting on it.