Ministers are considering replacing controversial control orders with new ways of restricting terror suspects.
Lord Macdonald, who is overseeing a review of counter-terrorism laws, told MPs "a lot of work" had been done on possible alternative schemes.
He also refused to repeat his past opposition to control orders and said he was keeping an "open mind".
The orders can include 16-hour curfews, electronic tags, travel and mobile phone curbs and were created in 2005.
Control orders - in which terrorist suspects are placed under close supervision, which some compare to house arrest - were brought in to replace the detention without trial of foreign suspects, which the law lords ruled breached human rights.
Former Director of Public Prosecutions Lord Macdonald, now a Lib Dem peer and the independent overseer of the Home Office's review of counter-terrorism and security powers, was questioned by the home affairs committee on Tuesday.
He refused to repeat his previous opposition to control orders, saying he came to the process with an "open mind" and, having "had sight of the most classified material", said it was possible he could change his stance.
"It's obviously possible in the light of evidence which has been gathered by this very extensive inquiry, this very careful inquiry, that one's views will change.
"One of my purposes is to see precisely that people within government, the people in the agencies, come to this inquiry with an open mind so that they too are prepared to change their minds."
He told the committee "many options" were being considered.
"One is to keep control orders as they are, one is to abolish them entirely, and the other is to replace them with some other scheme which is different from control orders but provides some form of reassurance.
"I think there is scope for all those things. You can make arguments for each one of those options. Certainly a lot of work has been done on possible schemes that might replace the control order scheme."
He also confirmed the review would not be published before Christmas.
The Liberal Democrats are strongly opposed to control orders, but the security services argue that they are a vital tool in the fight against terrorism.
The BBC's deputy political editor James Landale said that, after the criticism the Lib Dems had received for accepting a rise in tuition fees, Deputy Prime Minister Nick Clegg would face more pressure if he failed to abolish control orders.
The previous Labour government argued it had to control some suspects who could not be prosecuted because secret intelligence is not allowed in British trials.
But shadow home secretary Ed Balls indicated last month that, if police and security services could persuade the home secretary that alternatives such as travel restrictions and increased surveillance could work, Labour should support a change.
Before the election the Conservatives pledged to review control orders while their coalition partners the Lib Dems promised to scrap them completely.
When they entered into coalition they ordered the review, which has been carried out by the Office for Security and Counter-terrorism - that operates from inside the Home Office.
Last month former shadow home secretary David Davis told the BBC that about 25 Lib Dem MPs and possibly as many Tories would oppose moves to keep control orders, amid predictions that the review would recommend that they be kept.