Mr Clegg said no party could be "in cahoots" with another
The Lib Dems insist they have not made up their mind about what they would do if the general election fails to give one party a majority in Parliament.
The Guardian reports leader Nick Clegg is "planning to rule out" a formal coalition with Labour or the Tories.
But a Lib Dem spokesman said it had not planned for "hypothetical situations".
The party would have to get a formal coalition deal past its members and may opt instead to back Labour or the Tories on a vote-by-vote basis.
Deputy leader Vince Cable told BBC Radio 4's World at One that a hung Parliament could be "in the national interest" because "it could force parties to work together in a way that single-party government wouldn't".
Opinion polls are currently suggesting a hung Parliament is the most likely outcome - something that has not happened after a British general election since 1977, when the Liberal Party formed a "Lib/Lab pact" with Labour Prime Minister James Callaghan.
There has been much speculation about whether the Lib Dems would enter into a similar deal with Labour or the Conservatives if neither wins an overall majority of seats in Parliament.
WHAT IS ALTERNATIVE VOTE?
Voters rank candidates in order of preference and anyone getting more than 50% in the first round is elected.
If that doesn't happen, the candidate with the fewest votes is eliminated and their second choices allocated to the remaining candidates
This process continues until a winner emerges
The Guardian reports that Mr Clegg would not want his MPs to take up cabinet posts, but would instead use his greater influence to try to direct government policy.
The four key "shopping list" aims, mentioned by the Lib Dem leader in previous speeches, would be: more funding for education; more redistributive taxes; measures to create a "greener economy"; and political reforms including changes to voting and an elected House of Lords.
A Lib Dem spokesman said: "We have not ruled in or out any hypothetical situations after an election.
"The voters will decide the result of the election and then all parties will have to respond to that decision.
"In the meantime we will get on with our job of getting across the Liberal Democrats' policies to build a fairer Britain."
Mr Cable said the idea that the Lib Dems were planning to rule out a coalition was "the product of a vivid imagination".
He said: "We are not talking about deal-making... We are competing on the basis of our ideas and values and we want to win as many seats as we can."
Of the post-election period, Mr Cable said: "Our role in it will be constructive. We will act in the wider national interest."
Last month, Mr Clegg said he was not the "king-maker" who would decide whether Labour or the Tories rule in the event of a hung Parliament.
He told the BBC there would be no "backroom deals" ahead of the election and that politicians could not make such decisions "before people have their say" at the polls.
In recent months, both Prime Minister Gordon Brown and Conservative leader David Cameron have highlighted areas of agreement between their parties and the Lib Dems, on issues ranging from constitutional reform to civil liberties.
The government has promised a referendum on bringing in the alternative vote system - which would end the first-past-the post system under which MPs are elected - if it wins the general election.
The Commons backed the move last week, but it is not certain the proposal will become law before Parliament is dissolved ahead of the election.
A Lib Dem amendment to hold a referendum earlier and on a different voting system - the single transferable vote - was defeated by MPs.
Former Lib Dem leader Sir Menzies Campbell, who is close to Mr Clegg, said it was hard to see his party offering support to a Labour government that had just lost, or to a Tory party that refused constitutional reform.
But he told BBC Radio 4's The Westminster Hour: "If the alternative vote were on offer, and by that I don't mean a referendum or a Speaker's Commission but if legislation was agreed, that is certainly something to which we should give the most serious consideration."
The government is trying to get legislation on to the statute book for a referendum on alternative vote next year, but the Conservatives have ruled out electoral reform and backed the current first-past-the-post system.
If Mr Clegg does want to coalition with another party he will need the backing of his party's membership at a special conference.
The Conservatives are reported to be planning for the possibility of a second general election this year in the event of a hung Parliament, with them as the largest party.
Tory MP Andrew Mackay, until recently David Cameron's political and parliamentary adviser, told BBC News he believes Mr Cameron would form a minority government, set out a programme to tackle the economic crisis, and challenge the other parties to back him or vote him down with the prospect of asking the Queen to dissolve parliament for another election if he were defeated on a crucial vote.