Putin, speaking to reporters after talks with Finnish President Tarja Halonen, also accused the Baltic countries of discriminating against their Russian-speaking minorities.
Asked whether he would like to continue as president after his second term ends in 2008, Putin said, "Maybe I would have liked to, but the Constitution does not allow it.
"I'm of the opinion that the most important issue in Russia now is stability, and the only way to achieve this is by respecting the Constitution."
There has been persistent speculation that Putin or his supporters in parliament might seek to amend the Constitution to allow a third term, although Putin himself has denied intentions of seeking a change to the Constitution.
Putin criticized Latvia and Estonia for rules that made it difficult for Russian speakers to gain citizenship.
"Our partners in the Baltic countries have invented the term 'noncitizen,' which doesn't exist in modern judicial systems, and in some documents they have used the term 'alien.' We think that it doesn't fulfill the requirements of the European Union," Putin said at a joint news conference on the lawn of Halonen's summer residence, in Naantali, 200 kilometers west of Helsinki.
Halonen dismissed Putin's criticism, saying the issue had been settled in line with European Union requirements. She said it would not be on the agenda when Finland took over the six-month presidency of the EU in July 2006.
"In both Estonia and Latvia, this has been sorted out. What I am particularly pleased about is that people have been encouraged to apply for citizenship and there are clear signs that the number of citizens has increased," Halonen said.
Many Russian speakers have either chosen not to apply for citizenship in the Baltic countries or have complained that Baltic language requirements are too stringent and that not enough teaching is available in Russian.
Latvian Foreign Minister Artis Pabriks called Putin's comments "ideologically based and hypocritical. ... They don't reflect the real situation in the Baltic countries."
"Human rights and minority rights are better in Latvia and Estonia than they are in Russia," Pabriks said in Riga.
After the news conference, Halonen whisked Putin to a nearby harbor in a golf cart before visiting the southwestern city of Turku, where the presidents lunched and visited the biotechnology department at Turku University. After arriving for his two-day working visit on Monday evening, Putin held talks at Halonen's summer residence before dining and having a sauna and "a beer" with Halonen's husband, Pentti Arajarvi.
The two presidents talked for several hours about questions of mutual concern, including economic cooperation, development of faster railway connections and canal routes, as well as customs inspections and patrolling the 1,300-kilometer Finnish-Russian border. Putin later left on a reserve Il-62 plane after the Il-96 that he arrived on experienced a mechanical problem just before takeoff, Interfax reported. He arrived in Moscow Tuesday evening.