Early results show that putting doctors and hospitals on a budget — a payment method promoted as a way to curb health costs — has not saved money in Massachusetts, Attorney General Martha Coakley concluded in a report released yesterday. One reason, an investigation by her staff found, is that providers with market clout still appear able to negotiate high payments, just as they do under the traditional system that pays them a separate fee for each procedure or visit. The yearlong review of what six large Massachusetts insurers paid providers in 2009 found that doctors working under the new "global payment'' system — which puts them on a per-patient monthly budget — generally did not cost less than doctors paid the standard way. And in some cases, large doctors groups such as Atrius Health and Mount Auburn Cambridge were far more expensive than physicians paid under the fee-for-service system, despite being put on a budget.