New Delhi, April 22 (PTI) : Candidates who clear the prestigious civil services examination will be considered only for the central government services they opt for and not others, the Union Public Service Commission (UPSC) has said.

Citing the change in rules, the commission has also asked candidates who have qualified for the civil services (main) examination, 2014, to list a new order of preferences of services they intend to join after their final selection.

"The candidates will be mandatorily required to fill up their revised service preferences during the period April 20-27, 2015," the UPSC said.

The candidates can give their preference for as many services as they desire to join. The UPSC said that aspirants should note that he or she would not be considered for allocation to the service for which they do not indicate any preference.

"If a candidate gives revised order or preference only say for IAS, IFS, IRS (IT) and IA&AS, then he or she will be considered for allocation to IAS, IFS, IRS (IT) and IA&AS only. In case, he or she does not get allocation to IAS, IFS, IRS (IT) and IA&AS on the basis of his or her rank, preference, medical status, availability of vacancy in his category at his turn etc, he or she shall not be considered by the government for allocation to any of the remaining services participating in the civil services examination," the UPSC said.

It has advised candidates to be "very careful" while indicating preferences for various services or posts.

The results of the main examination 2014 were declared on April 12. The department of personnel and training (DoPT) on April 10 notified new rules for the civil services examination under which candidates are required to list a revised order of preference after they clear the main test.

"If he is not allotted any one of the cadres for which he has indicated preference, he shall be allotted any of the remaining cadres in which there are vacancies after allocation of all the candidates who can be allocated to those cadres in accordance with their preferences," the notification said.

Candidates need to register on the commission's website (www.upsc.gov.in) using their roll number to get a new password, which would be forwarded on their registered e-mail. In case they do not wish to opt for a service or services, they will have to mark "99" against it, the UPSC has said.

The UPSC is India's central agency authorised to conduct a host of exams, among them civil services examination, engineering services examination, combined defence services examination, national defence academy examination.