WASHINGTON — Taking an aggressive stance on Iran in his bid for president, Mitt Romney is calling on New York state’s new comptroller to divest public holdings in companies linked to the Iranian government.

Mr. Romney’s campaign said yesterday that the former Massachusetts governor sent letters urging divestment to the comptroller, Thomas DiNapoli, Governor Spitzer, and Senators Clinton and Schumer.

“With your new responsibilities overseeing one of America’s largest pension funds, you have a unique opportunity to lead an effort to isolate Iran as it pursues nuclear armament,” Mr. Romney said in the letter to Mr. DiNapoli. “I request that you immediately launch a policy of strategic disinvestment from companies linked to the Iranian regime.”

The Republican presidential hopeful cited the bipartisan passageof a bill in the House calling for state pensions to divest from companies giving financial support to Iran’s energy sector. The letter did not mention any specific investments by New York’s $140 billion pension fund in companies linked to Iran.

A spokesman for the comptroller’s office, Daniel Weiller, said last night that to his knowledge, Mr. DiNapoli had not received any correspondence from the Romney campaign. Aides to the governor and the two senators did not return messages last night.

A spokesman for Mr. Romney, Kevin Madden, said the former governor chose to contact New York officials because the state has one of the largest public pension funds, and since Mr. DiNapoli is new to the job, “it presents a unique opportunity for a new policy of divestment from Iran.” A former assemblyman, Mr. DiNapoli, a Democrat, took office earlier this month after Alan Hevesi resigned amid scandal.

Mr. Romney’s new focus on New York came a day after Mayor Giuliani opened a wide lead over the former governor in a nationwide Quinnipiac University poll. Among Republicans, Mr. Giuliani had 40% support, Senator McCain of Arizona had 18%, and Mr. Romney stood at 7%. A former House speaker, Newt Gingrich, registered 10%, though he has not entered the race.

The letters also coincided with a speech Mr. Romney was set to give in Spartanburg, S.C., last night focusing on divestment as a means of economic sanctions against Iran. He has sought to make an aggressive approach toward Iran a cornerstone of his foreign policy platform. Messrs. Giuliani and McCain have also spoken out repeatedly against Iran, and both traveled to South Carolina, an early primary state, this week.

In a speech in Israel last month, Mr. Romney called for economic sanctions “at least as severe” as those imposed on South Africa during the era of apartheid. He also said the military option should remain “on the table” to prevent Iran from developing nuclear weapons, and he urged an indictment of President Ahmadinejad — who has called for wiping Israel off the map — for incitement to genocide.

In his letters yesterday, Mr. Romney pointed to Iran’s support for terrorist groups and recent evidence that indicates it is aiding militias in Iraq. “By eliminating financial support that helps fuel programs targeting our nation and our allies, America’s leaders can take action against this growing threat,” he wrote.

The Romney campaign also noted that last month, Mr. Romney helped arrange a meeting between a former Israeli prime minister, Benjamin Netanyahu, and the Massachusetts treasurer to discuss divestment of pension funds.