Lib Dem leader Sir Menzies Campbell has called for a "violent crimes" register and an end to the automatic release of prisoners halfway through sentences.
In a speech, he also said people in jail for serious crimes should continue to be denied the right to vote - a reversal of the party's past policy.
And he argued that foreign criminals must serve sentences in their home country or be deported on release.
He is trying to counter Labour and Tory claims his party is too soft on crime.
"A party which is serious about social justice cannot fail to be serious about preventing crime and enforcing the rules," he said.
Shift in policy
Sir Menzies is using a series of major policy speeches to outline the direction in which he wants to take the party.
Speaking to Lib Dem councillors in London, he signalled a sharp shift in approach to law and order from that of Charles Kennedy, who resigned in January.
He is setting up two policy groups to look at new ways for tackling crime.
A senior party aide admitted that, under Mr Kennedy, there had been "ambiguities" in the Lib Dems' handling of crime that had contributed to a public perception of the party as soft.
SIR MENZIES' PLANS
New register for violent offenders
Serious prisoners should continue to be denied the right to vote
Released foreign prisioners should face movement restrictions if they cannot be deported
End to automatic early releases
Sir Menzies told BBC News he did not think his party was "wishy washy" on law and order but said Tony Blair had tried to create that perception.
Without criticising Mr Kennedy directly, Sir Menzies made clear he thought the former leader was wrong when he said during last year's election campaign that child murderer Ian Huntley should have the vote.
People who had committed crimes like murder, rape or manslaughter should forfeit all rights to vote, he argued.
"If you break the law to that extent you should not be allowed to vote for those who make the law," he told BBC Radio 4's Today programme.
Aides said Sir Menzies was not abandoning official party policy that some inmates should be granted the vote.
Sir Menzies responded to the recent string of serious crimes - including the murders of banker John Monckton and teenager Mary-Ann Leneghan - committed by convicts on parole.
He called for the establishment of a violent offenders register to help police and other law-enforcement agencies keep track of dangerous people.
And he urged an end to automatic release for prisoners who have served half of their sentence, insisting that parole boards must be given discretion on when an inmate should go free.
Sir Menzies says offenders such as Ian Huntley should lose their vote
Sir Menzies said the plans should cut, not push up, prisoner numbers by making new efforts to rehabilitate prisoners.
"Prison should be for those who have to be kept there but it should not be used as it were as a dumping ground," he said.
"For too many people are in prison who do not get in prison the sort of retraining and rehabilitation which would enable them to lead useful lives outside."
Sir Menzies attacked Home Office mismanagement amid continuing controversy over the foreign prisoners freed without being considered for deportation.
But junior Home Office Minister Joan Ryan said: "Ming Campbell's words have not been backed up by Lib Dem action. His party is still soft on crime and soft on thugs.
"If Ming Campbell is truly to lead his party in a new direction he will have to make sure his party in Parliament votes for the practical measures needed to tackle the problems we all acknowledge remain."