More than 7,000 police will be on hand, cordoning off parks and other sections of central Athens, to keep demonstrators away from the German leader who is due to arrive in the Greek capital at 1:30 p.m. (1030GMT) Tuesday for talks with conservative Prime Minister Antonis Samaras.
Many of Europe's leading politicians have avoided official travel to Greece and the risk of a hostile reception, as the debt-saddled country struggled to keep up with commitments needed to guarantee rescue loan payments and long-term euro membership.
But Merkel, heading Europe's largest bailout contributor, accepted Samaras' invitation to Athens despite failure by his government so far to conclude a massive new austerity package. The cuts will save (EURO)13.5 billion ($17.5 billion) but doom Greece to a sixth year of recession in 2013.
After months of tough rhetoric, the German chancellor may be preparing her own voters for a more tolerant approach toward Greece ahead of federal elections next year, according to Jason Manolopoulos, author of the 2011 book on Europe's financial crisis, "Greece's Odious Debt."
"Given how some other members of the (eurozone) core—Austria, Holland, Finland—had made some very harsh comments ... I think it does send a message to Greece," Manolopoulos said of Merkel's visit.
"But I think it's also important, if not more important, for German domestic consumption."
In Athens, Merkel will meet with Samaras and President Karolos Papoulias, the largely ceremonial head of state, in adjacent buildings before flying back out of the country.
Draconian security measures include a ban on public gatherings outside the German Embassy and other parts of central Athens as well as within 100 meters (330 feet) of her motorcade route from the airport.
Samaras' own partners in his coalition government described the police measures as excessive. And Greece's main labor union, the GSEE, called them a "display of force ... aimed at canceling our democratic rights" insisting it would go ahead with plans to stage a 1:00 p.m. (1000GMT) rally near parliament.
Late on Monday, about 2,000 people attended a peaceful demonstration around Athens' main square to protest Merkel's visit.
Greece's debt crisis started in late 2009 after it misreported deficit figures, triggering fears that debts in other eurozone countries may also be at risk.
Since May 2010, the country has depended on bailouts from the eurozone and the International Monetary Fund.
But to get the loans, it implemented successive pay cuts and tax hikes, while increasing retirement ages and facilitating private sector layoffs that are expected to push the rate of unemployment up next year to nearly one in every four workers.
"These measures are hitting every Greek family—hurting our children," Nikos Papageorgiou, head of a hotel workers' union in greater Athens said at Monday night's rally.
"People should not be afraid to protest because of the police measures. No one can deny us the right to ask for a better life."
Efty Katsareas in Athens contributed.