WASHINGTON (Reuters) - Defense Secretary Robert Gates has warned the White House the United States lacks an effective strategy to curb Iran’s steady progress toward nuclear capability, The New York Times reported on Saturday, citing officials familiar with the document.

Defense Secretary Robert Gates discusses changes to the Pentagon's "Don't Ask, Don't Tell" policy prohibiting homosexuals from serving openly in the U.S. military during a media briefing in the Pentagon Briefing Room in Washington, March 25, 2010. REUTERS/Hyungwon Kang

Gates’ secret memorandum was sent in January to President Barack Obama’s national security adviser, General James Jones, and it touched off an intense effort inside the Pentagon, the White House and the U.S. intelligence agencies to develop new options for the president.

Those options included a revised set of military alternatives, still under development, to be considered should diplomacy and sanctions fail to force Iran to change course.

In that case, Iran could remain a signatory of the Nuclear Nonproliferation Treaty while becoming what strategists call a “virtual” nuclear weapons state, the newspaper said, citing U.S. officials familiar with the document.

Among his concerns, Gates included the lack of a response should Iran choose the course that many officials and analysts consider likely -- assembling all the major parts needed for a nuclear weapon, such as fuel, designs and detonators, but stopping just short of assembling a fully operational weapon.

Officials familiar with the memo’s contents described only portions dealing with strategy and policy and not sections that apparently dealt with secret operations against Iran, or how to deal with Persian Gulf allies, The Times said.

One senior official described the document as “a wake-up call,” the newspaper said, adding that White House officials disputed that view and insisted that for 15 months they had been conducting detailed planning for many possible outcomes regarding Iran’s nuclear program.

The Times said Gates spokesman Geoff Morrell declined comment on specifics in the document but issued a statement on Saturday saying, “The secretary believes the president and his national security team have spent an extraordinary amount of time and effort considering and preparing for the full range of contingencies with respect to Iran.”

A senior administration official told The Times there was a line Iran would not be permitted to cross.

The official said the United States would ensure that Iran would not “acquire a nuclear capability,” a step Tehran could get to well before it developed a sophisticated weapon.

Jones told The Times on Friday that the Obama administration did have a strategy on Iran.

“The fact that we don’t announce publicly our entire strategy for the world to see doesn’t mean we don’t have a strategy that anticipates the full range of contingencies,” he said. “We do.”