In some respects, Iran's program is more advanced than Iraq's was under Saddam Hussein. But the administration seems content for the time being to rely on international pressure rather than military threats to curb Iran's ambitions.
Officials hope to enlist the U.N.'s International Atomic Energy Agency as an ally. IAEA officials have been making monthly visits to Iran. State Department spokesman Richard Boucher said the administration is looking forward to a full report by the Vienna-based agency at a board of governors' meeting next month.
Boucher said Iran's activities could lead to uranium- and plutonium-based nuclear weapons.
"We have long made clear our serious concern about Iran's active pursuit of nuclear weapons as well as other weapons of mass destruction and longer range missile delivery systems," he said.
Boucher rejected Iran's contention that its nuclear activities are for peaceful purposes.
"Iran admitted to constructing a uranium enrichment plant and a heavy water plant only after it had no choice because this had been made public," he said.
There's no evidence the Iranians have actually begun enriching uranium, but, as CBS News National Security Correspondent David Martin reports, outside experts like David Albright believe they are close.
"Within a few years they can make nuclear weapons if they choose to," Albright tells CBS News.
The plant, he says, "was built in a 70-foot-deep hole so it was deliberately built underground in order to withstand an aerial attack, so you really have to wonder what the purpose of it is."
In Vienna, diplomats who commented on the condition of anonymity said the United States has raised the issue with Russia, France, Britain, Germany and other members of the 35-nation IAEA board.
Washington is specifically seeking a declaration from the board that Iran has violated the nuclear Nonproliferation Treaty, which it has signed.
A declaration, depending on its language, could restrict itself to an expression of concern about a violation or increase pressure on Tehran to account for its activities by referring the issue to the Security Council.
The United States and Russia have argued for years over Iran's intentions and whether Moscow has been a key contributor to Iran's nuclear programs.
Earlier this week, Russian Deputy Foreign Minister Alexander Losyukov said there was no evidence that Iran was pursuing a nuclear weapons capability.
He made the comment in response to appeals by Under Secretary of State John Bolton during a Moscow visit for Russia to support an IAEA report critical of Iran.
Losyukov said Russian-Iran cooperation was "strictly in line with IAEA norms."
An administration official, asking not to be identified, said a nuclear-armed Iran would become a threat to all of its neighbors. Adding to U.S. concern are Iran's links to international terrorism, the official said.
He said Iran has missiles capable of going 1,300 kilometers and is developing longer range models which can reach beyond the Middle East and into Europe.
Boucher said that contrary to Iran's claims, there is no economic justification for Iran's nuclear program.
"Iran flares off more gas annually than the equivalent energy its desired reactors produce," Boucher said.