US President George Bush acknowledged Saturday that he has personally authorized a secret program that allowed wiretapping American citizens as part of the war against terror. The announcement, delivered by Bush in his weekly radio address, followed mounting pressure from lawmakers demanding explanations for the plan that is seen as infringing on the basic civil liberties of American citizens. The eavesdropping program, which was first reported by The New York Times on Friday, played a major role in the administration's defeat in its attempt to extend the US Patriot Act - a post 9-11 measure designed to lift restrictions from wiretapping and gaining access to private records of terror suspects. Four Republican lawmakers joined the Senate Democrats in blocking the bill, which expires on December 31. The revelation of Bush's secret eavesdropping program aimed at American citizens was cited as the main reason that led Senate Republicans to cross the lines and call for revising the Patriot Act before approving its extension. Bush, in a harshly worded statement, confirmed the Times report, but defended the secret program, labeling it "crucial to our national security." The president added that the wiretaps were authorized only in order to intercept communication of individuals who have a clear link to al-Qaida or other terror groups, and that his administration reviewed the authorization every 45 days. "This authorization is a vital tool in our war against the terrorists. It is critical to saving American lives. The American people expect me to do everything in my power, under our laws and constitution, to protect them and their civil liberties and that is exactly what I will continue to do as long as I am president of the United States," Bush said in his radio address. He added that the intelligence personnel conducting this program were highly qualified and specially trained on issues of civil liberties. Bush said in his announcement that the wiretaps were crucial in preventing terror activists in the US from communicating with their operators overseas and gave an example of such communication that were conducted from San Diego before the 9-11 attacks against the US. Despite the heavy political price he is paying due to the secret wiretap program, President Bush made clear he would not consider stopping it "as long as our nation faces a continuing threat from al-Qaida and related groups." While Bush said his decision to authorize the wiretap plan was legal and constitutional, Democratic lawmakers claimed the president had no authority to allow a US government agency to eavesdrop on American citizens without any court order. Senator Russell Feingold, a Wisconsin Democrat, called the president "King Bush" and said that "this is not the system of government that we have and that we fought for." The president had harsh words for those who talked about the program to the media, saying their actions were illegal and improper. "As a result, our enemies have learned information they should not have," he said. "The unauthorized disclosure of this effort damages our national security and puts our citizens at risk." Opponents of renewing the law argue that it threatens constitutional liberties at home. However, most Republicans and other supporters say the act is essential for protecting the country against terrorists. Some of the most contentious elements of the Patriot Act include powers granted to law enforcement agencies to gain secret access to library and medical records and other personal data during investigations of suspected terrorist activity. The law also allows the government to conduct roving wiretaps involving multiple phones and to wiretap "lone wolf" terrorists who may operate on their own without control from a foreign agent or power. If the law is not renewed, its powers will expire only for new investigations of people whose criminal activity begin following that date and who were not associated with anyone who was already under investigation. AP contributed to this report.