NEW YORK (Reuters) - New York's Mayor Bill de Blasio announced on Wednesday an agreement on a balanced $82.1 billion city budget for the 2016-2017 fiscal year that boosts reserves and expands a summer youth employment program.

The agreement was reached with New York's City Council and comes well ahead of a July 1 deadline. De Blasio, a Democrat, said it was the earliest agreement since 2001 and credited the cooperation between his administration and the City Council.

The agreement increases reserves, with an additional $250 million to grow the Retiree Health Benefits Trust Fund to $3.9 billion. It includes $1 billion every year in general reserves, and $500 million in the capital stabilization reserve.

The budget highlights de Blasio's social mission. The executive budget, presented in April, dedicated $2 billion to overhauling the city's $7.5 billion public hospital system, which treat around 1.4 million people per year.

City Council Speaker Melissa Mark-Viverito and other council members hailed the expansion of the city's summer youth work program to 60,000 at a press conference at City Hall. The program places young people aged 14-24 with community organizations for summer employment.

The budget agreement comes at a difficult time for de Blasio who is facing multiple investigations into his campaign finances.

On Wednesday the head of New York City's prison guard union and a hedge fund financier were charged with operating a kickback scheme. It marked the first major prosecution to emerge from state and federal corruption probes examining de Blasio's fundraising practices, among other avenues of inquiry.

(Reporting by Edward Krudy; Editing by Andrew Hay)