LONDON, May 14 (Reuters) - Britain's healthcare cost-effectiveness agency NICE said on Wednesday that a Johnson & Johnson prostate cancer drug, originally invented in Britain, was not worth giving to patients who have yet to receive chemotherapy.

Although Zytiga, or abiraterone, is already cleared for use in some men after chemotherapy, a green light for its earlier use would allow many more patients to access the oral medicine.

"We know how important it is for patients to have the option to delay chemotherapy and its associated side effects, so we are disappointed not to be able to recommend abiraterone for use in this way," Andrew Dillon, chief executive of the National Institute for Health and Care Excellence (NICE), said in a statement.

"However, the manufacturer's own economic model showed that the drug would not be cost-effective at this stage - because of this we cannot recommend the drug in this preliminary guidance."

Zytiga, which is given as a daily tablet, costs 2,930 pounds ($4,900) for 120 tablets.

Paul Workman, deputy chief executive of Britain's Institute of Cancer Research, whose scientists discovered the drug, said he was disappointed by the decision and he urged NICE, the state health service and J&J to reach a deal on a fair price as soon as possible.

"Abiraterone has in part been a victim of the success of prostate cancer medicine, since men who have not yet received chemotherapy now live for longer than two years, meaning NICE could not apply its end of life criteria," he added.

NICE, which must decide if treatments offer value for money for the public health service, is frequently chastised for not recommended expensive new cancer drugs. In an effort to address some of these concerns it introduced a more lenient appraisal system for drugs given at the end of a patient's life.

($1 = 0.5939 British pounds) (Reporting by Ben Hirschler; Editing by Greg Mahlich)