UNITED NATIONS (Reuters) - The 193-member United Nations General Assembly has agreed a core budget of $5.4 billion for the next two years, marginally smaller than the amount allocated for 2014/2015, as top contributor the United States pushes for improved efficiency and cost management.

The core U.N. budget, down from $5.5 billion in the previous two-year period, was agreed by the General Assembly late on Wednesday. It does not include peacekeeping - which has a separately negotiated budget of $8.27 billion for the year to June 30, 2016 - or the costs of several major U.N. agencies funded by voluntary contributions from member states.

"The budget you have approved reflects the difficult global financial reality we have faced for a number of years," U.N. Secretary-General Ban Ki-moon told the assembly. "Funding continues to shrink while demands on the United Nations grow."

The United States, which is the top contributor and pays the maximum 22 percent, said a number of funding cuts and improvements in efficiency had been made and the 2016/2017 budget was a "great step forward" for reforming management and budgetary practices.

"For the first time in 26 years, the committee adopted a staff compensation package that slows previously-mounting staff costs, which had hindered service delivery," said a U.S. official.

"The elimination of 150 redundant posts is a further step in the direction of the organization's efficiency, as are 5 percent reductions in supplies, travel, and furniture and other equipment costs," the official said.

Other top contributors for 2016/2017 will be Japan with 9.68 percent, China 7.92 percent, Germany 6.38 percent, France 4.85 percent, Britain 4.46 percent, Brazil 3.82 percent, Italy 3.74 percent, Russia 3.08 percent and Canada 2.92 percent.

(Reporting by Michelle Nichols; Editing by Alistair Bell)