BANGKOK (Reuters) -- Thai Prime Minister Thaksin Shinawatra defended his business and political track record on Saturday, vowing to stay on as protesters gathered for the largest anti-government rally in 14 years.

Thaksin pleaded with supporters in a weekly radio address to stay away from the rally in central Bangkok, which was organized by friend-turned-foe Sondhi Limthongkul, to avoid any clashes. "I won't give up," Thaksin said in a defiant tone. "Most importantly, I won't let down those who have voted for me and have so much faith in me."

Sondhi, a media tycoon who began his anti-government campaign after his talk show was axed from state television in September, called for the rally to oust Thaksin, whom he accused of running the country for the benefit of his own and his cronies'.

Sondhi told Reuters on Friday he was hoping an uproar over the $1.9 billion sale of Shin Corp, the telecoms empire Thaksin founded, could push the number of protesters over 100,000, though the government expected crowds in the tens of thousands.

At least 3,000 police were to be deployed to maintain order at the Royal Plaza, a ceremonial square one block away from Thaksin's office at Government House.

The Nation newspaper, which has leapt on the Shin Corp share sale by Thaksin's family as a chance to attack him, said the rally could be the biggest since May 1992 protests against the military junta of General Suchinda Kraprayoon. Then, dozens of people were killed in a week of clashes with soldiers.

Thaksin spent most of his 50-minute radio address talking about the legitimacy of his family's sale of its Shin Corp holdings -- which he had handed over to his children on entering politics -- and argued that it did not need to pay taxes on the capital gain.

Thaksin, denying his policies favored his business, said Shin Corp stock rose in line with the main Stock Exchange of Thailand index over the past five years, while shares of other top firms outperformed the index by as much as fourfold.

Citing his second landslide election victory last February, Thaksin said King Bhumibol Adulyadej -- who has no formal power under Thailand's constitutional monarchy -- was the only person he would heed. "If His Majesty whispers to me and says 'Thaksin, you should go', I will immediately pay respect to his feet and quit."