Olmert flew to Washington on Sunday for his first meeting as prime minister with President Bush. The two leaders are expected to discuss Iran's nuclear ambitions.
The key issue regarding Iran was not when it builds a nuclear bomb, but rather when it acquires the knowledge they need to manufacture such arms, Olmert said in a televised interview.
"This technological threshold is nearer than we anticipated before. This is because they are already engaged very seriously in enrichment," Olmert said.
"The technological threshold is very close. It can be measured in months rather than years," Olmert added, repeating statements previously made by other senior Israeli officials.
Olmert said the world could not take Iran's nuclear ambitions lightly because Iranian President Mahmoud Ahmadinejad has repeatedly called for Israel's destruction. However, he said it was unlikely Israel would act on its own, diplomatically or militarily, to deal with the problem.
In 1981, Israel's air force attacked the Iraqi nuclear reactor at Osirak, destroying the facility. But Olmert said the situations cannot be compared, and Israel will try to persuade the Western world to impose sanctions on Iran.
Iran has so far rejected European proposals to back off the idea of U.N.-imposed sanctions if Tehran agrees to freeze its uranium enrichment program. Another proposal the Europeans are preparing will apparently include a clause saying that if Iran refuses, it could face sanctions backed by the threat of force.
Iran, which insists its nuclear program is for peaceful, civilian purposes, says it has the right to enrich uranium.
Olmert expressed confidence that Bush would "lead other nations in taking the necessary measures to stop Iran from becoming a nuclear power."
"We will certainly try to convince other countries that, at this time, before they cross the technological threshold, that the measures will be taken to stop them," Olmert said.