April 22 (Bloomberg) -- Australia won't reduce its quarantine requirements to speed the flow of imports needed to replace crops and livestock lost to drought, Prime Minister John Howard said today.

The nation, the world's third-largest wheat exporter and the second-biggest beef shipper, is in the grip of its worst drought in a century. The potential closure of the country's biggest inland waterway for irrigation won't lead to a relaxation of the controls on the extra imports that would almost certainly result, Howard said.

``We're not going to put the security of our agriculture sector at risk by arbitrarily waiving quarantine and bio- security requirements,'' he said on the Australian Broadcasting Corp.'s Landline Program.

Irrigation from the Murray-Darling river system, which runs through five states and territories and supports half the country's cropping land, will be halted to maintain town water supplies unless there is significant rain in the next two months, the government said April 19.

The region's 50,000 farms generate more than 40 percent of the nation's income from agriculture and grazing, and account for about three-quarters of all the country's irrigated land.

Australia's weather forecaster predicts only a 50 percent chance of average rainfall over most of the country in the next three months.

While farm incomes can't be underwritten, most growers in the Murray-Darling basin can get assistance from the government's Exceptional Circumstances program, which provides financial support and interest rate subsidies, Howard said.

The government is also meeting with farming leaders to consider other help it can offer during a crisis ``unprecedented in my lifetime,'' he said.

``It's very serious,'' Howard said. ``We should all literally, and without any irony, pray for rain.''

To contact the reporter on this story: Gavin Evans in Wellington at gavinevans@bloomberg.net

Last Updated: April 22, 2007 03:34 EDT