MR Patten seems not to have his mind on his job. How else to explain his decision last night to ''release'' two illegal immigrant girls from prison (but into the care of the Social Welfare Department) while others remain in jail? Either that, or he is too ready to accept the advice of his publicity machine and tackle a high-profile problem without bothering to find out the full extent of the Government's own policy and actions. His quick fix to the embarrassment of the imprisonment of Au Yeung Ling-ling, 14, and Tong Hiu-kwan, 17 - both held in custody for months while waiting to appear as court witnesses - is designed to polish his image as a human rights supporter. But it deflects attention from the much more embarrassing truth that Hong Kong routinely locks illegal immigrants behind bars for months at a time while they wait to give evidence in someone else's court case, without charging them with any crime. Further, in contravention of the Bill of Rights, it fails to separate juveniles from adults. All this is sanctioned under the territory's Draconian immigration legislation. But it is out of tune with the lip service this administration pays to human rights. The Governor's gesture fails to bring relief to dozens of other illegal immigrant witnesses, including juveniles, being held in custody. So little thought had been given to their fate that the Governor's spokesman was yesterday unable even to say if there were any at all. The gesture also fails to tackle this bad law. The Governor has so far ordered the Secretary for Security and the Attorney-General only to look into ways to speed up trials involving detained witnesses and to make special arrangements for juveniles. He has ordered no review of the legislation. The most charitable way to look at Mr Patten's intervention is that he had not thought the matter through. A less pleasant interpretation is that last night's decision is a device to mislead human rights campaigners and has no long-term implications. How very cynical.