OTTAWA - Prime Minister Stephen Harper offered an 11th-hour compromise Monday to salvage two controversial weapons in the government's anti-terrorism arsenal.

And his justice minister, Rob Nicholson, said he's open to other possible compromises. But the Liberals dismissed all the gestures as too little, too late.

Without support from the Liberals or other opposition parties, the government is poised to lose a vote Tuesday on a motion asking Parliament to renew for three years the preventive arrest and investigative hearing provisions of the Anti-terrorism Act.

Without parliamentary approval to renew, the provisions will automatically expire on Thursday.

The two measures are part of the previous Liberal government's response to the Sept. 11, 2001, terrorist attacks on the United States. They empower authorities to arrest and detain suspects without charge and to compel testimony before a judge.

In a bid to secure Liberal support, Harper offered to adopt a proposal recommended by a Liberal-dominated Senate committee last week.

Like the government's motion, the committee recommended a three-year extension of the two measures. But it added a stipulation: that an annual report on the use of the measures include an explanation as to whether the provisions remain warranted.

"I think the Senate's proposed a couple of things that are realistic,'' Harper said after floating the compromise in the Commons.

"We want to see something. So, you know, we're open to getting something done here. It's important to have the anti-terrorism provisions that are effective.''

In the Commons, Harper taunted Liberal Leader Stephane Dion for "flip-flopping'' on legislation introduced by his own party. He then challenged Dion to accept "a compromise suggested by his own colleagues'' in the Senate.

Dion, who maintains the provisions are an unnecessary infringement on civil liberties, wouldn't budge.

"The prime minister must understand we cannot extend (the measures) today and worry about rights tomorrow,'' he told the Commons.

If Harper was serious about finding a compromise, Dion said, he would have instigated a comprehensive overhaul of anti-terror legislation months ago, rather than jumping on last-minute Senate proposals.

"It's a complete improvisation,'' Dion said later.

With New Democrat and Bloc Quebecois MPs expected to unanimously oppose renewal of the measures, the minority Tories would need at least 30 Liberals to break ranks to win Tuesday's vote.

While a few Liberal MPs are unhappy with Dion's position and remained unsure Monday of how -- or if -- they'll vote, the new leader's insistence on a united front appears to have quelled most dissent. Dion said he expects "strong discipline and strong solidarity'' in Tuesday's vote.

Nicholson said he's willing to revisit a compromise floated by dissident Liberals last week and rejected by Dion: extending the anti-terrorism measures for only nine months, or even just six months.

"Our goal is to make sure that police have the tools that they need to fight terrorism in this country,'' he said.

Dion contends that the two provisions should not be dealt with in isolation but rather as part of a comprehensive package of reforms to anti-terrorism laws, as proposed by Commons and Senate reviews of the legislation.

Nicholson dismissed that position as unrealistic given the Mar. 1 deadline for renewing the two provisions.

"We can't come up with a major piece of legislation ... overnight,'' he said.

Nicholson said he's willing to consider some reforms in future. But there's little chance the Liberals will trust the government to act in good faith later if they agree now to renew the two measures.

"We're not prepared to take the prime minister at his word,'' said Michael Ignatieff, Liberal deputy leader.

Ignatieff said the government has had six months to act on recommendations of the Commons committee that reviewed the Anti-Terrorism Act. Yet only now is the government "showing a little movement and we're saying it's a little bit late.''

The probable demise of the two provisions comes less than a week after the Supreme Court of Canada struck down another weapon in the government's anti-terrorism arsenal. The court struck down security certificates, used to detain and deport non-citizens suspected of terrorism, as a violation of fundamental rights.