The US is planning to site interceptor missiles and a radar station in Poland and the Czech Republic.
It says the shield is needed to protect Europe from possible rocket attacks by "rogue states" such as Iran and North Korea.
Putin is constitutionally obliged to step down as Russian president when his term ends in six months time.
There had been suggestions that the Russian leader planned to revive plans to merge Belarus with Russia and give himself a position above that of a national president.
"I wouldn't be surprised if Putin tries to speed up a union with Belarus ... to become the president of the unified state," Gennady Zyuganov, the Russian Communist Party leader, said earlier this week.
Russia's Ekho Moskvy radio also speculated on the merger, quoting unidentified members of the Lukashenko administration as saying Moscow and Minsk had struck a deal on a Russia-Belarus union.
The radio reports said under the merger Putin would become president while Lukashenko would be speaker of its parliament.
But on Friday, Lukashenko dismissed suggestions the leaders would discuss plans for a unified state during their two-day meeting.
Lukashenko said he was "surprised" Putin's visit had "triggered such a fuss" and said he expected the meeting to be unremarkable.
"There are no political connotations here. We are friendly and allied states and I would be surprised if there was no official visit. There is nothing extraordinary here,"he said.
The Kremlin also moved to quash talk of an imminent merger, denying the talks would touch upon a draft constitution for a merged state.
On Monday, Putin announced his support for Dmitry Medvedev, his protege, to become Russia's next president and Medvedev in turn asked Putin on Tuesday to be his prime minister, though Putin has not yet accepted.
Western analysts have argued that the role of prime minister would be unappealing for Putin.
But many doubt a merger deal between Russia and Belarus could be reached, saying Lukashenko, often referred to as Europe's last dictator, is unlikely to cede power.
"The two nations have opposite interests," Alexander Klaskovsky, a Minsk-based independent political analyst, was quoted by The Associated Press as saying.
"Moscow wants to expand its presence in Belarus, while Minsk wants to get economic assistance while maintaining full sovereignty."
In the 1990s, Lukashenko pushed for the creation of a single state, apparently hoping to take over from Boris Yeltsin, then Russian president, as the Soviet Union crumbled.
Putin's election in 2000 put an end to Lukashenko's hopes and two years later the Belarusian leader rejected a Kremlin proposal for incorporating his nation into Russia.
Although relations are sometimes strained between the two leaders, Lukashenko, who is barred from most Western countries, counts Putin as one of his few allies.
Russian newspaper Vremya Novostei said the most pressing issue at the meeting would be renewed talks on Russian credit to help Belarus pay mounting bills for Russian natural gas.