Labour MP Anne Begg warned there was a danger that the "wrong" candidate could be elected if there was confusion over which party to back.
In a BBC interview, Mr Kennedy said he believed that Liberal Democrat and Labour supporters would look at voting patterns in their constituencies before deciding who to back.
He said: "What is quite clear is that all three parties will have their target seats at the next election and their activists will, understandably, tend to give their attention to that.
"People can make up their own minds, particularly based on the results of the last election."
Independence restated
Mr Kennedy said his party would fight the election as an independent force while maintaining its "constructive oppositionist" stance towards the Labour government.
"We are going into the next election on our own basis, making quite clear there is a great deal to be disappointed about with the Blair administration but that, under their present policy platform, a return to a Conservative government would be a disaster for the interests of this country," he said.
Despite Mr Kennedy's apparent support for tactical voting in some cases, there are indications that many party activists in both Labour and the Lib Dems remain hostile to the idea.
Labour MP Anne Begg warned there was a danger that the "wrong" candidate could be elected if there was confusion over which party to back.
"Tactical voting is fine in theory and as an intellectual discussion in the drawing room or living rooms around the country, but when you actually get to polling day and you have to vote against your principles, then it is much harder to do," she told BBC Radio 4's World at One programme.
Dilemma
Ms Begg said that it was a dilemma she had faced herself in the past and felt unable to back either the Scottish Nationalist or Tory candidates over Labour.
Earlier in the year fellow Labour MP Denis MacShane published a list of 127 Tory seats which he argued could fall either to Labour or the Lib Dems in the event of people casting their votes tactically in favour of whichever party came second in 1997.
During the Romsey by-election, the Lib Dems took what was thought to be a safe Conservative seat in what was then interpreted to be an example of tactical voting by Labour supporters.