But he cautiously welcomed the accord struck in Geneva at the weekend, which will also open industrial markets and boost global growth and has restored the credibility of the World Trade Organisation's (WTO) by putting its Doha Round on track.
"The early signs are that there has been a change of heart by the Europeans and the Americans regarding subsidies. I say early signs because I have seen these things in the past and they have turned out to be false dawns," Howard told Australian radio.
"But there is an agreement to talks in detail about an agreement and it's positive news, but I don't think people should get over excited about it because there's still a long way to go," he added.
After five days of wrangling, the WTO's 147 member states agreed a framework laying down the guidelines for the round, which has been in trouble since the collapse of talks almost a year ago in Cancun, Mexico, when no deal on subsidies was found.
Australia, one of the world's largest agricultural commodity exporters, has long pressed the European Union and the United States to roll back subsidies and wants greater access to the 15-nation market.
The EU, in turn, accuses Australia of claiming to be a free trade champion while using strict quarantine laws to bar imports.
Australia and the United States signed a bilateral free trade deal in February, but the pact angered Australia's farm industry after it only gained reductions on beef exports over 18 years and a small rise in the duty free quota for dairy products exports.
Yet, Howard said it was important that the deal relaunching world trade talks showed that Australia's deal with the United States had in no way affected or reduced the country's capacity to deal with key trading blocs for a multilateral agreement.