The most expensive mayor's race in U. S. history is getting pricier by the minute, already at $23 million and still soaring.

Between them, Democrat John F. Street and Republican Sam Katz have raised $7.7 million since the spring's primary, according to campaign finance reports filed yesterday with the city commissioners.

Street has raised more than Katz, $4.1 million versus $3.6 million, since early June. With two weeks to go before the election, Katz had more in the bank, $1.4 million vs. $723,000 for Street.

But with unprecedented levels of television ads already purchased, it appeared that each campaign has more than enough money to saturate the airwaves, fill voter mailboxes with campaign literature and dispatch modest battalions of street workers on Election Day.

"We're fully competitive," said Street spokesman Ken Snyder. "Short of buying each and every voter a large cheese pizza, I think we've done everything we wanted to do."

"We have had enough money to do everything we wanted," echoed Katz's campaign manager, Bob Barnett.

Previously unreported contributions to Katz included $100,000 from Warren Musser, chairman of Safeguard Scientifics, and $50,000 from Dennis J. Alter, chief executive officer of Advanta Corp., and his wife, Gisela.

Several major Katz donations came from past supporters of Democrat Happy Fernandez, including $25,000 from Elizabeth Woodward of Chestnut Hill and $20,000 from businessman Bernard Spain.

Top contributors to Street in the past month included developer Mark Mendelson of Hampton Realtors, who gave $50,000; broker Arnold M. Katz of Brokerage Concepts, $35,000; the law firm Ballard Spahr Andrews & Ingersoll, $30,000, and the Metropolitan Council of Carpenters, $25,000.

The third candidate in the mayor's race, John McDermott of the Constitutional Party, reported he was $44 in the red, raising $3,025 and spending $3,069 through mid-October.

The new figures from Street and Katz pushed total spending in the mayoral contest past $23 million, going back to the beginning of 1998 and counting all six contenders for the Democratic nomination last spring.

The total sets a new record for spending by big-city mayoral candidates, according to a Daily News survey of campaign finance rules in the nation's big cities.

The record was previously held by Los Angeles, where 24 mayoral candidates spent an estimated $21.5 million in 1993, a race won by Republican Richard Riordan.

Among the nation's 10 biggest cities, Philadelphia and San Antonio, Texas, are the only ones with no restrictions on how much individuals can donate to a candidate for mayor.