Immigration chiefs are revoking the passports of 5,000 rapists, prostitutes, murderers and other criminals after a lax screening programme allowed them to become US citizens. The Immigration and Naturalisation Service (INS) is braving the severe embarrassment of having allowed them to become citizens of the land of the free - and telling its critics in Congress that it will not happen again. The announcement of the revocation of so many citizenships in one fell swoop is highly unusual, since the INS is normally only able to take away American nationality from around 20 immigrants a year. The administration has argued that the 5,000 slip-ups are only a fraction of the nearly one million new Americans who were given passports last year. But it has also admitted that there are a further 180,000 applicants whose criminal backgrounds were never properly checked and whose cases will have to be reviewed. The issue has become a political hot potato for the White House because Republicans allege that the problem has arisen from a politically motivated programme to naturalise as many new immigrants as possible before the 1996 presidential and congressional elections. New immigrants tend to vote Democrat by an overwhelming margin. The speeded-up naturalisation process, which began in 1995, was called Citizenship USA and heralded as a means of expediting procedures and clearing a large backlog of people with naturalisation claims. But the programme soon became mired in accusations that the INS was not carrying out its own stringent guidelines in making extensive background checks on the past records of the immigrants - most of whom have emigrated from Latin and Central America. Republican Congressman Lamar Smith praised the INS for finally taking action to resolve the problem. But he also warned: 'One convicted felon who is given the honour of becoming a citizen of our country is one too many.' The authorities also face a long legal fight - not only in taking back the passports, but deporting some of the most serious criminals. Immigrants in such cases routinely hire lawyers who are able to drag the cases through the courts, sometimes for years. Signs that the INS knows it is in for a long, expensive fight can be seen from the fact that it has asked Congress to grant it extra funding to hire lawyers and clerks to deal with the pile of cases.