A day after Ralph Nader announced he is running for president, a potential independent candidate, Mayor Bloomberg, declared there’s no such thing as a spoiler and said time is running out for third-party contenders to get into the race.

“This business of Ralph Nader being a spoiler — you know, in any three-way race, two of the three are going to be spoilers,” Mr. Bloomberg said. “Come on. Everybody’s got a right to do it — you’re not spoiling anything.”

“If people want to vote for you, let them vote for you, and why shouldn’t they?” he added.

The billionaire 66-year-old mayor denies he is exploring his own presidential bid, but aides and operatives have been working behind the scenes to lay the groundwork for an independent campaign, should he decide to jump in and fund it with his own fortune.

Without the need to raise money, Mr. Bloomberg has been able to delay a decision much longer than most candidates.

Many Bloomberg watchers have been eyeing March 5 — next Wednesday — as a key date on his timetable because it is the first day that he would be able to start a petition drive to get on the ballot in Texas, which has one of the earliest deadlines and some of the toughest requirements for independents.

Asked today at his regular news conference whether it’s too late for third-party candidates to be entering the race, Mr. Bloomberg gave a long answer that showed he is well-informed about the intricacies of ballot access rules.

In recent months he has sought the advice of ballot access experts like Clay Mulford, who served as campaign manager for another billionaire third-party candidate, Ross Perot.

“It’s getting close to being too late,” Mr. Bloomberg said today. “It would take a lot of money, which Ralph Nader doesn’t have, to get on all the ballots … some states make it difficult, some states make it easier.”

Still, he said, Mr. Nader has every right to try.

“I’ve just never understood why, just because you’re a member of a party, you have special rights,” Mr. Bloomberg said. “That’s not the civics that I learned in junior high school, and if Ralph Nader wants to run, good luck to him.”

Mr. Bloomberg associates said this month that the mayor may end up launching petition drives in a handful of states before he has made a final determination about whether to run.

His advisers have said he could put off a decision as late as May.

Mr. Bloomberg spoke about Mr. Nader in response to questions today in the Bronx, where he was holding a news conference about electronic health records.