Howard's move, which mirrors the push by U.S. President George W. Bush to outlaw gay marriage across the United Sates, follows new laws by the self-governing Australian Capital Territory (ACT) to allow same-sex unions.
National laws in Australia say a marriage must be between a man and woman at the exclusion of all others, but the ACT laws would have given gay couples the same legal rights as married couples by describing the marriages as "civil unions". "Our view is very simple. We are not prepared to accept something which is a plain attempt to equate civil unions with marriage," Howard told reporters.
Mr Ruddock said, even with amendments to the civil union laws designed to address the federal government's concerns, the ACT was being deliberately confrontational.
"This issue could have been dealt with in a way that was not deliberately as confrontational as it was," he said.
His ACT counterpart, Simon Corbell, said the federal government was "homophobic". Bush wants the U.S. Senate to pass a constitutional ban on same-sex marriage after several state courts since 2003 ruled that state legislatures did not have the right to ban it.
Canada became the fourth country to legalise same-sex marriage in mid-2005 but the new conservative government will allow a free vote in parliament to decide whether the laws should be overturned.
Australia's centre-left Labour opposition said Howard was wrong to intervene over laws passed by the democratically elected ACT government, which administers the nation's capital Canberra.
"The law should recognise caring and loving relationships," Labour spokeswoman Nicola Roxon said, adding that gay couples continued to be discriminated against in areas such as pensions, tax and health and welfare benefits.
Guide to Same Sex Marriage in Australia - Wikipedia