BERLIN, Germany (CNN) -- Angela Merkel was sworn in Tuesday as Germany's eighth post-World War II leader and its first female chancellor, taking an oath of office that commits her to "dedicate my strength to the welfare of the German people."

The inauguration ceremony in parliament formally sealed the conservative Merkel's rise to power after lawmakers elected her chancellor on a vote of 397-202, with 12 abstentions.

Merkel, who succeeds Gerhard Schroeder, is also the first former East German to lead her country.

She heads a right-left "grand coalition" that joins her center-right Christian Democrats (CDU) and their sister Christian Social Union (CSU) with Schroeder's Social Democrats (SPD).

But about 50 of Schroeder's Social Democrats voted against her, indicating dissent among the coalition's ranks.

Schroeder was the first to walk over and congratulate a smiling Merkel after the vote was announced.

"Dear Mrs. Merkel, you are the first democratically elected female head of government in Germany," parliament president Norbert Lammert said.

"That is a strong signal for women and certainly for some men, too. I wish you strength, God's blessing and also some enjoyment in your high office."

The parliamentary vote came six months after Schroeder announced he was seeking national elections a year early, plunging Germany into a period of political uncertainty.

An inconclusive election forced Germany's largest parties into talks, and it took two months after the vote to reach the end result.

Merkel's CDU/CSU won the September 18 elections by a razor-thin plurality in the Bundestag, or lower house of parliament, forcing the parties to form a "grand coalition" with Schroeder's SPD.

After weeks of negotiations, the two blocks reached agreement on measures aimed at fighting 11 percent unemployment, controlling spending and reforming the government.

But some SPD members opposed some of the measures, including loosening labor market rules. Their votes against the coalition could mean trouble ahead for a government with a four-year mandate.

Pastor's daughter

Merkel, 51, was born in Hamburg but grew up in East Germany as the daughter of a pastor.

She joined the pro-democracy movement in the waning days of the communist era, then rose through the ranks of the Christian Democrats under then-Chancellor Helmut Kohl.

Polls show many Germans are unconvinced the CDU leader will last a full four-year term because of the tough coalition deal she had to strike with the SPD.

The SPD finished a close second and secured half of the 16 seats in Merkel's Cabinet, including the high-profile finance and foreign affairs portfolios.

Merkel was forced during the hard coalition talks to abandon a planned major shake-up of the German social welfare system that had been a cornerstone of her economic reforms.

The new chancellor bargained away key campaign pledges such as limiting union power in regional wage negotiations and accepted a Social Democrat demand for a "rich tax" on top earners.

However, the Social Democrats' parliamentary leader said he was convinced the new government would succeed.

"For that we require a strong chancellor," Peter Struck, defense minister under Schroeder, told The Associated Press. "The foundation stone will be set with the election of Ms. Merkel."

Merkel has vowed to resuscitate the economy -- once Europe's motor but now one of the most sluggish in the 25-nation European Union -- and cut unemployment that hit post-war highs under Schroeder.

Merkel also wants to repair relations with the United States, strained by Schroeder's vocal opposition to the U.S.-led war in Iraq.

After Tuesday's vote in parliament, she and her Cabinet were sworn in and formally took over from the SPD-Greens coalition government that Schroeder led for the past seven years.

Her clinical, almost shy approach, has been mocked in the German media, but some commentators, Reuters says, believe it is tailor-made for a coalition that bridges right and left and requires delicate handling.

"Her dislike of the theatrical in politics, of the show and big words, fits with the new sobriety of Germany's younger generation," the German daily newspaper Handelsblatt said in an editorial on Tuesday.

One of Merkel's first engagements will be in Paris to meet French President Jacques Chirac Wednesday -- and then on to Brussels to meet EU officials.

She is flying to London on Thursday to meet British PM Tony Blair. The EU budget is certain to be among topics discussed.

Schroeder said he will step down from his Bundestag seat Wednesday to return to private life.