The Navy’s nuclear-powered aircraft carriers, barred from city waters for nearly two decades by a policy enacted under Mayor Dinkins, may soon be gracing New York City’s waters again.

“I would love to have big ships and I personally don’t see any risk whatsoever,” Mayor Bloomberg said yesterday at an event in Brooklyn.

The Navy is now retiring its last conventionally powered aircraft carriers, such as the USS John F. Kennedy, which has visited New York in the past, and many of the Navy’s newer ships are unable to dock in New York for Fleet Week celebrations due to an unwritten ban on nuclear-powered or nuclear-armed vessels. According to Mr. Bloomberg, enough time has passed since the policy was enacted in 1990 to reconsider its merits.

“I think the understanding of nuclear technology and the safety of it is a lot different than it was during the Dinkins days,” Mr. Bloomberg said yesterday. “What may or may not have been appropriate then, may or may not be appropriate today.”

While some have attributed this year’s record-low ship count for Fleet Week to the antinuclear policy, the mayor said the war in Iraq, which draws ships to the Persian Gulf, was the primary factor. The Navy has previously denied reports that military operations in Iraq, which have been under way since 2003, have limited the number of ships for Fleet Week.

“The fact that we have fewer ships this week is not because of the David Dinkins decision,” Mr. Bloomberg said. “We have a war going on overseas. Whether you like the war or not, the simple fact is that the military has to deploy its resources to protect this country and, in the case of the Navy, to support our troops on the ground. That is their first priority — that should be their first priority.”

Mr. Bloomberg’s support for reopening the city’s waterways to nuclear vessels drew praise from Mayor Koch, who said he would “of course” back such a move. As mayor, Mr. Koch was a strong supporter of a plan by President Reagan’s Navy secretary, John Lehman, to build a homeport on Staten Island that would house Navy ships. Opponents of the ultimately unsuccessful plan said the Navy’s refusal to rule out docking nuclear-armed and -powered ships at the port presented a safety risk to the city if an accident were to occur. This led Mr. Dinkins to institute the nuclear ban, which Mr. Koch yesterday said he opposed.

“When I was mayor, I announced New York would be the homeport for any U.S. ships — nuclear or otherwise — and with pride,” Mr. Koch said in an interview. “It’s an outrage that there are New Yorkers who believe that the rest of America should defend New York City with our nuclear-powered Navy and should say no.”

Others were less enthusiastic about the prospect of nuclear vessels entering the city for future Fleet Weeks, citing safety concerns.

“Allowing nuclear reactors to be docked in Manhattan seems like an unnecessary risk,” Council Member Eric Gioia, a likely candidate for public advocate in 2009, said yesterday via e-mail.

Council Member Bill de Blasio of Brooklyn said that while the nuclear ban’s origins reflected the politics of another period, a cautious approach to changing it might be in order.

“Clearly, if the mayor is reflecting upon the fact that we live in very different times, he’s very right. When Mayor Dinkins was elected this was the end of the Cold War and this was related to a very strong disarmament movement in the 1980s,” Mr. de Blasio said yesterday in an interview. “But if he wants to change the policy, I think it should be re-examined carefully.”

Mr. Dinkins did not respond to several messages requesting comment yesterday.