WASHINGTON (AP) _ Hillary Rodham Clinton and New York Mayor Rudolph Giuliani each has spent millions on what likely will be history's costliest U.S. Senate race.

Giuliani raised $8.8 million over the last six months, according to papers his campaign filed Monday with the secretary of the U.S. Senate. He spent $4.4 million last year _ more than many Senate candidates have even raised so far.

Giuliani collected a total of $11.5 million last year, outpacing the first lady, who only began fund raising in July.

Mrs. Clinton's aides estimate she has raised about $8 million. Her report was not immediately available Monday.

A detailed account of who contributed and where the campaigns spent money was not available. That information is contained in massive reports the campaigns must file with the Federal Election Commission that had to be postmarked by Monday. Only summary pages were made available by the campaigns.

Giuliani had $7.4 million cash on hand at the end of 1999, according to his filing.

Although it was unclear specifically where Giuliani has spent his cash, aides have said that about $700,000 went for a television ad campaign. The Giuliani camp also has spent money on a direct-mail campaign to solicit donations. Many of those fund-raising letters have appealed to conservatives and have taken shots at Mrs. Clinton.

Most of Giuliani's contributions came from individual donors. But his campaign also raised $245,311 from political action committees _ $178,536 of that in the last six months.

Anthony Corrado, a government professor who specializes in campaign finance at Colby College in Maine, said the race was on track to be the most expensive political contest in U.S. Senate history. He said the difference is the millions of dollars that will be spent by the political parties and outside interest groups, which isn't included in the filings.

``We're looking at a level not seen in previous Senate races,'' Corrado said.