On the eve of President Obama’s major speech on the rationale for going to war in Libya, senior officials say the joint military effort there is going well.

But they add that additional US weaponry might be needed to attack Muammar Qaddafi’s forces on the ground, and they hold out the possibility that it might be months before the military mission is over.

Speaking on several Sunday television news shows, Defense Secretary Robert Gates and Secretary of State Hillary Clinton increased the rhetorical pressure on Qaddafi – and on his closest aides, who might be persuaded to abandon him.

The administration is "sending a message to the people around him," Sec. Clinton said on NBC's Meet The Press. "Do you want to be a pariah? Do you really want to end up in the international criminal court? Now is your time to get out of this and to help change the direction."

While the no-fly zone is well-established and air attacks on Qaddafi’s armored units have allowed rebels to take key cities, Sec. Gates said, defeating Libyan military units might have to involve new air assault weapons and tactics – including attack helicopters and the AC-130 gunships able to rain down heavy cannon fire on enemy troops and equipment.

Concern for civilian "collateral damage"

But to the extent that Qaddafi forces take shelter in urban areas, even ground attack weapons more precise than bombs and cruise missiles risk causing “collateral damage,” i.e. civilian deaths and injuries.

That’s one reason why the US is considering whether to provide arms to the rebels, Gates said. But asked on ABC's This Week if the US military might be involved in the fighting through 2011, he said, "I don't think anybody knows the answer to that."

Critics in Congress and elsewhere have questioned the importance of Libya to US national security as a reason for going to war there.

On ABC, Gates acknowledged that Libya is “not a vital national interest to the United States.”

But Gates, Clinton, and Obama in his radio address Saturday insisted that the situation in Libya is important to US interests – including stability in the Middle East and northern Africa.

“I firmly believe that when innocent people are being brutalized; when someone like Qaddafi threatens a bloodbath that could destabilize an entire region; and when the international community is prepared to come together to save many thousands of lives, then it's in our national interest to act," Obama said Saturday.

While Obama and senior administration officials keep insisting that Qaddafi must go, making that happen for a dictator who’s held onto power through fear, bribes, and tribal manipulation for 42 years is not easy.

Should Qaddafi himself be targeted?

That’s raised the question of targeting Qaddafi for assassination, a possibility put forth over the weekend by former UN Ambassador John Bolton – a man with a reputation for being exceedingly hawkish, even within the Bush administration.

In his closed-door meeting with members of Congress Friday, Obama said there are no plans to use the US military to assassinate Qaddafi, according to Politico.com.

Over the years, presidents of both parties have issued executive orders banning the assassination of foreign leaders. But executive orders, which do not have the force of law, can be reversed.

Following the 1986 bombing of a German disco, which killed two American servicemen and injured dozens more – and which was blamed on Libya, based on intercepted messages – then-president Ronald Reagan ordered retaliatory strikes against Tripoli and Benghazi.

Qaddafi survived the attack on his compound, but scores of other people were killed, including the Libyan leader’s 15 month-old daughter.

Twelve years later, Qaddafi apparently retaliated. Libyan agents under orders from Qaddafi planted a bomb on Pan Am Flight 103. The explosion over Lockerbie, Scotland, killed 270 people on the passenger jetliner and on the ground.

More recently, the opening days of “shock and awe” air attacks on Baghdad in 2003 included Saddam Hussein’s various residences as targets – unsuccessfully, as it turned out.

A week ago, one of the scores of highly-accurate cruise missiles launched from US Navy ships in the Mediterranean Sea slammed into a building in Qaddafi’s compound.

Was that an attempt to kill Qaddafi?

No, US officials say, it was just a place where a military command-and-control facility happened to be.