Senate Majority Leader Bill Frist urged President Bush on Friday to intensify efforts to put interceptor missiles at a site in Europe to protect against potential attacks from Iran.

"The threat from Iran is only going to grow in the years ahead. We need to take steps now to prepare to deal with that threat," Frist, R-Tenn., said in a letter to the president.

"The time has come to revive and reinvigorate discussions with allies in Europe that have previously expressed interest in hosting these interceptors at a third site on their territory," said Frist, who is retiring from the Senate and is considering running for president in 2008.

The United States has interceptor missiles buried in California and Alaska to counter potential threats from the Pacific, including from North Korea. The Bush administration has spent more than a year negotiating with several European allies to find a third site for the ground-based interceptor missiles, including discussions last year with Poland.

The U.S. Missile Defense Agency did not immediately return a call seeking comment on Frist's suggestions.

Countrywatch: Iran

In the letter, Frist sought to send a signal to Iran that the United States is committed to countering that country's nuclear ambitions. At the same time, the potential presidential candidate aimed to show that he's strong on national defense, which could be a major issue in the White House race two years from now.

Putting interceptor missiles at a site in Europe would significantly enhance the United States' ability to protect against ballistic missiles launched from Iran, Frist said in the letter.

"As Iran continues to make progress in deploying its Shahab 3 missiles and developing new, longer range missiles, while simultaneously pursuing nuclear weapons, the ability to shoot down Iranian warheads in flight becomes increasingly critical to our national security," Frist said.

His comments came as the United States and European allies continue their efforts to persuade Tehran to roll back its uranium enrichment program that can produce fuel for nuclear power generators or the material for nuclear warheads.

Iran insists that its program is peaceful.