NEW DELHI, India (AP) _ India's Supreme Court ordered the city of New Delhi on Thursday to immediately begin phasing out diesel-burning buses and convert the capital's transportation fleet to cleaner compressed natural gas by Jan. 31.

At least 9,000 of 12,000 municipal buses still run on diesel, two years after the court first ordered public vehicles to switch to compressed natural gas.

The court has previously criticized the inaction of the agencies involved in the conversion process, saying they had no concern for a pollution-free environment, the right of every citizen.

At its last hearing on the issue, the court had given the New Delhi authorities until Thursday to come up with a plan to convert public buses to compressed natural gas, to make sure enough of the fuel is available, and, in the meantime, to check that the diesel being sold in the city of 13 million is pure.

The court had said that it would give a new deadline, and on Thursday declared that by Jan. 31, 2002 all city-owned buses must be running on compressed natural gas.

The city has missed several previous deadlines.

Drivers of buses, taxis and auto-rickshaws have staged several strikes _ leaving millions of commuters stranded _ to protest the court's orders.

While owners of most taxis and three-wheeled auto-rickshaws have converted their vehicles to run on compressed natural gas, they often wait in line for hours to get it.

It's one-third cheaper than gasoline, but the city has authorized only one company to supply it, at a few stations.

Buses, used by most travelers, have been slower to convert.