WASHINGTON (Reuters) - The United States will pledge $400 million (201 million pounds) in aid to Kosovo next week at a donors conference expected to raise more than $1 billion for the newly independent state, a senior U.S. official said on Wednesday.

The donors conference aims to strengthen the government of the former Serbian province, which declared independence in February, nine years after NATO bombing drove out Serb forces because of their ruthless tactics against an insurgency.

"The United States is going to throw in $400 million over the next four years," Assistant Secretary of State Dan Fried told reporters of the U.S. pledge at the donors conference to be held in Brussels on July 11.

"We expect total pledges of well over $1 billion which will ... help the Kosovar government get off to a good start," he added.

Kosovo, whose population is 90 percent ethnic Albanian, declared independence on February 17 after nine years under U.N. administration and is still in the process of establishing its governing institutions.

Some of its ethnic Serb minority, supported by Serbia and Russia, bitterly opposed independence but the declaration has produced relatively little violence in the latest step in the tortuous break-up of Serb-dominated Yugoslavia over the last two decades.

The Bush administration requested the bulk of its pledge from the U.S. Congress more than a year ago, well before Kosovo declared independence, out of a certainty that the region would need financial help whenever it declared independence.

A U.S. official who asked not to be named said that the of the $400 million U.S. pledge, Congress has already approved about $291 million.

He said the money will go toward debt relief to help Kosovo when it assumes part of Serbia's sovereign debt.

It will also help to establish governing institutions such as the police, the judiciary and government ministries and to spur economic growth through job creation programs, he said.

(Reporting by Arshad Mohammed; editing by Jackie Frank)