WASHINGTON — Major world powers agreed yesterday to pursue new sanctions against Iran, even though the watered-down penalties already levied by the United Nations have only made Iran rush faster to perfect nuclear expertise.

America and other nations fear such expertise could one day lead to a bomb.

New sanctions are probably months away, and Tehran is running out the clock on the Bush administration in hopes of getting a better offer from a new American president next year.

“We see this as a stalling tactic,” a State Department spokesman, Gonzalo Gallegos, said of the short, vague reply Iran delivered early yesterday to the latest invitation from a European diplomat who has tried for years to lure the clerical regime into negotiations.

America and a fragile partnership of countries that do business with Iran are trying to buy out the most sophisticated part of the oil giant’s nuclear program, leaving Tehran able to produce energy but not bombs. Iran says it isn’t seeking weapons and won’t scale back a legitimate energy-production program.

Iran didn’t rebuff the latest offer outright, and as usual there were several interpretations of the regime’s motives. Iran is showing new signs of openness to talks, but any bold move may come only after Mr. Bush leaves office.

The decision to seek further penalties came in a conference call linking the European Union foreign policy chief, Javier Solana, with senior diplomats from the five permanent members of the U.N. Security Council, as well as Germany, the State Department said.