By Marc Jones

LONDON (Reuters) - One of the world's most influential bond market voices has warned that the dollar’s position as the world's reserve currency could be lost unless the United States gets its spending under control.

Jeffrey Gundlach, chief executive of DoubleLine Capital and dubbed the "bond king" due to a history of timely market calls, said the risk came as high interest rates continued to ramp up the $33.59 trillion worth of U.S. national debt.

"Should the Federal Reserve continue to raise rates, which may happen, or should the national debt grow, which is certain to happen, this problem will get much worse," Gundlach said in an opinion piece.

"The future of the U.S. dollar and possibly out-of-control inflation depends on getting the budget and spending under control."

Gundlach, whose firm oversees around $150 billion of assets under management, said the interest rate on U.S. debt could rise to 5.5% over time given the current level of Federal Reserve borrowing costs.

This would increase the country's annual interest bill alone to $1.8 trillion a year, which is more than double the current U.S. defence budget.

In just over two years, that interest expense has risen from $500 billion to nearly $900 billion which is already far more than is spent on defence, Gundlach added.

"The massive budget deficit and increasing interest rates on the national debt should scare every American," he said.

(Reporting by Marc Jones; Editing by Toby Chopra)