The move was certain to alarm the West which has criticised the oil-rich nation on the Caspian Sea for not showing enough commitment to democratic change, but Nazarbayev's supporters said it would ensure stability and investment continuity.
The Central Asian state's parliament voted overwhelmingly last week to allow Nazarbayev, in power since 1989, to run again for the presidency and stay in office for an unlimited number of terms.
In a constitutional article saying the president is elected for two terms, the amendments, published in the Kazakhstan Pravda newspaper on Tuesday, said ''This limitation does not apply to the First President of the Republic of Kazakhstan.'' The nation's fragmented opposition denounced the move as undemocratic. Kazakhstan has never held elections judged free and fair by international monitors.
''There are certain elements of Nazarbayev's (personality) cult in this,'' said Aidos Sarimov of the opposition-linked Altynbek Sarsenbaiuly think tank.
''Nazarbayev wants to show that 'I am still here, ... I am still the boss here.'' The move was also likely to put a question mark over Kazakhstan's bid to take over the rotating chairmanship of the Organisation for Security and Cooperation in Europe (OSCE) in 2009.
Nazarbayev, 66, whose current term expires in 2012, has not said when or whether he plans to stand aside or who might succeed him in the nation bordering Russia and China.
His allies have said prolonging Nazarbayev's term would help the country ensure stability in the otherwise volatile Central Asian region. One top official said it would ''only be a blessing for our nation, for our young independent state.'' But the move was all but certain to disappoint those in his entourage who have put their bets on replacing him, and hushed all talk about Nazarbayev preparing to pick a successor.
The opposition has long accused him and his family of tightening their grip over most aspects of life in the former Soviet nation, from key government posts to industry.
Most media do not criticise Nazarbayev and the opposition movement is weak. Two opposition leaders were killed in mysterious circumstances in late 2005 and early 2006.
Nazarbayev's critics called the murders politically motivated.
The amendments included a number of constitutional changes the government has praised as a step towards democracy.
That included raising the number of parliamentary deputies, cutting presidential terms to 5 years from 7 and allowing parliament to play a bigger role in picking the prime minister.
REUTERS AE VV1248