American First Lady Hillary Clinton has formally declared that she is running for the US Senate in New York.

Accompanied by husband Bill and daughter Chelsea, she made her long-expected announcement at a presidential-style rally near her new home in suburban Chappaqua, New York.

"I may be new to the neighbourhood but I'm not new to your concerns," Mrs Clinton said.

She told 2,000 cheering supporters that she would fight to improve health care, education, child care and employment.

"Because I believe we can meet these challenges together, I am honoured today to announce my candidacy for the United States Senate from New York," she announced to a standing ovation.

Starting on Monday, Mrs Clinton will be a part-time first lady as she begins a long tour of the state and an exhaustive campaign leading up to the 7 November vote.

Tough contest

Although she made her intentions clear last November, her formal announcement is an indication that her campaign is now in full swing.

However, opinion polls give a narrow lead to her likely challenger, New York City Mayor Rudolph Giuliani.

He is still formally to declare, but says he is running, and correspondents say Mrs Clinton has a tough fight ahead of her.

In the last few weeks, she has appointed a high-profile advertising agency to help sell her message. Her first advertisement has been aired on local radio, and she has moved into her new home in the state.

But even in the Democratic stronghold of New York City, there are many who oppose Mrs Clinton - either because she is not from the state, or because they consider her tarnished by the Lewinsky scandal, or because they suspect her of political opportunism.

In an apparent effort, meanwhile, to share some of the day's political limelight, Mr Giuliani appeared on five Sunday morning television chat shows.

He said Mrs Clinton lacked sufficient experience of public office to be a senator and her positions were too "left-wing".

Mr Giuliani said he plans to run on his record as mayor and remind voters how the city's crime rate and welfare numbers have dropped dramatically in his seven years in office.