Governments are not doing enough to prevent terrorists from acquiring nuclear weapons, a former secretary of defense, William Perry, says, and he will deliver that message tonight in Midtown at a “teach-in” fund-raiser for the Nuclear Threat Institute.

“Nuclear terrorism is a real danger and a serious danger,” Mr. Perry, who served under President Clinton, told The New York Sun. “It’s real because there’s a reasonable probability of it happening, and serious because such an event would be catastrophic, especially in a city like New York.”

Many sites that house the chemicals needed to construct nuclear weapons are not adequately secured, Mr. Perry said.

Tonight’s fund-raising dinner, which will be held at the Harvard Club of New York City, is expected to bring in $1 million to support the institute’s efforts to thwart the use and the proliferation of nuclear, chemical, and biological weapons.

Launched in 2000 by a former chairman of the Senate Armed Services Committee, Sam Nunn, and the founder of CNN, Ted Turner, the NTI has provided $5 million to help secure a cache of poorly guarded enriched uranium outside Belgrade and spent $2 million to remove materials that could have produced as many as two dozen nuclear bombs.

Last year, in a partnership with the International Atomic Energy Agency, the NTI committed $50 million to create a fuel bank for countries that have decided against developing nuclear capabilities.

“The basic message is that a private organization such as NTI can contribute to reducing the threat from nuclear weapons, and we have a six-year track record of doing that,” the president and chief operating officer of the institute, Charles Curtis, said in an interview. “We made a difference — and we’re making a difference. The private sector needs to invest in its own security, and New Yorkers understand that better than anyone.”

A member of the institute’s advisory board, Frederick Iseman, a managing partner of a $2 billion private investment firm, Caxton-Iseman Capital Inc., is underwriting the fund-raiser. Mr. Iseman said the event is an opportunity to introduce the Washington-based institute’s work to a larger swath of New York corporations and residents. “The response has been very positive,” he said, noting the evening’s wide range of institutional sponsors. “We all have a vested interest in this.”

Corporate sponsors of the fundraiser include Credit Suisse, Goldman Sachs, and JP Morgan.

Mr. Nunn will also address the expected audience of about 200, as will the vice president of the NTI’s Russia/New Independent States Program, Laura Holgate, and a career Central Intelligence Agency officer, Michael Hurley.