According to an opinion poll published in the Mainichi Shimbun daily, 78% of Japanese lawmakers favoured some changes to the document, 57 years after it came into force.
A survey of ordinary citizens last week indicated 53% thought revision was needed.
Debate is heating up particularly over Article Nine which renounces the right to go to war and forbids a military, except when forces' role involves self-defence.
Japan, one of the closest US allies in Asia, has sent 550 ground troops to Iraq - in a strictly non-combat role - to help rebuild the war-torn country, its biggest and riskiest mission since World War Two.
Critics say the deployment violates the pacifist Article Nine, but others argue that change is long overdue.
"The world moves on, the region around Japan moves on, times change," said Yasuhiro Nakasone, a former prime minister and longtime kingpin in the ruling Liberal Democratic Party (LDP), in an interview with NHK national television.
"We have a responsibility to change the constitution to suit the times."
According to the Mainichi survey, 78% of 545 lawmakers from both houses of parliament who responded said the constitution needed revision.
However, opinions were divided about Article Nine.
While 70% of lawmakers felt no change should be made to the war-renouncing clause of the article, 57% felt that revision was needed to the clause that prohibits a military.
"A broad revision of the constitution is needed to fit with new values that have developed, as there are many sections that no longer suit the current era," said Shinzo Abe, LDP secretary-general, in a statement.
"A broad revision of the constitution is needed to fit with new values that have developed, as there are many sections that no longer suit the current era"
Secretary-general, Liberal Democratic Party
Debate on revising the constitution, once taboo, has picked up steam, with both the LDP and its main opposition rival seeking to draft their own proposals for revisions by 2005 and 2006 respectively.
Those pushing for revisions say they are needed, at least partly, to allow Japan's military a wider role in peace-keeping operations overseas, particularly under the aegis of the United Nations - where Japan has long hoped for a permanent seat on the Security Council.
"If we truly want to take a permanent Security Council seat, we can't just say our constitution doesn't allow things," said Fumio Kyuma, a senior LDP official.
The constitution was drafted by US occupation forces and adopted by Japan's Parliament. It went into effect on 3 May 1947.