BAGHDAD — President Ahmadinejad of Iran arrived today in Baghdad for the first-ever visit by an Iranian president to Iraq, waving as he stepped off his plane to be greeted by representatives of a nation that was once Iran’s bitter enemy.

The visit gives Mr. Ahmadinejad a chance to highlight the improved relationship his nation has with post-Saddam Hussein Iraq while also serving as an act of defiance toward America, which accuses Iran of aiding Shiite extremists in Iraq.

Among the delegation of Iraqi officials gathered at Baghdad international airport was Foreign Minister Hoshyar Zebari, who said that Mr. Ahmadinejad plans to leave tomorrow morning. Upon Mr. Ahmadinejad’s arrival, the group piled into a military convoy headed for a meeting at President Jalal Talabani’s residence.

Security was tight along the airport road, once among the most dangerous in this war-torn city, with Iraqi army patrols stationed every 100 yards or so. America has said it would not be involved in providing security for Mr. Ahmadinejad’s visit.

Mr. Ahmadinejad is scheduled to meet not only with Mr. Talabani but also Prime Minister al-Maliki, both of whom have made official visits to Iran since taking office. Mr. Talabani’s headquarters are located right across the Tigris River from the mammoth new American Embassy in the fortified Green Zone, an area that has been repeatedly hit by mortar attacks, with America blaming Shiite militants.

Iran and Iraq are both led by Shiite Muslims. The two countries were hostile to each other during Saddam’s regime and fought a long and destructive war during most of the 1980s. But Mr. Ahmadinejad sought to reassure Iraqis ahead of the trip that Iran is not fueling violence in Iraq.

“Iran has no need to intervene in Iraq. It is friendly to all groups in Iraq. Isn’t it ridiculous that those who have deployed 160,000 troops in Iraq accuse us of intervening there?” the Iranian state-run news agency, IRNA, quoted Mr. Ahmadinejad as saying.

With the trip, Mr. Ahmadinejad also may be trying to bolster his support back home ahead of parliamentary elections later this month.

They are seen as referendum on the Iranian president, who has come under criticism from all sides in his country for spending too much time on anti-Western rhetoric and not enough on economic problems plaguing the country.

The head of the Middle East program at Washington’s Center for Strategic and International Studies, Jon Alterman, said the visit sends a “clear message to Iraqis that the Iranian influence in the country is significant and enduring.”

But at the same time, “he doesn’t want to threaten the Iraqis. He doesn’t want to threaten Gulf states who fear that Iraq will be an Iranian satellite. He has a thin line to walk,” he said.

America has tried to downplay Mr. Ahmadinejad’s visit, saying it welcomed Iran’s stated policy of promoting stability but that its actions have been doing the opposite.

President Bush denied that Mr. Ahmadinejad’s visit undermined America efforts to isolate Tehran but had some advice for what Mr. al-Maliki should say to the Iranian leader.

“He’s a neighbor. And the message needs to be, quit sending in sophisticated equipment that’s killing our citizens,” Mr. Bush told reporters at his ranch in Crawford, Texas.