BERLIN (Reuters) - Leading members of Angela Merkel's Christian Democrats (CDU) are considering a U-turn in policy on same sex couples after a court ordered the government to grant them greater adoption rights, in an embarrassing ruling for the chancellor.

Germany's constitutional court ruled last week that gay people should be allowed to adopt a child already adopted by their partner, and that the present ban was unconstitutional because it violated the principle of equal treatment.

The court gave the government until July 2014 to amend the law, which applies to gay people in civil partnerships.

"We will of course implement the constitutional court's ruling - that is called for now. At the same time, we will see whether tax amendments are necessary," Volker Kauder, leader of the CDU's parliamentary group, told the Welt am Sonntag paper on Sunday.

At a party congress last December the CDU had thrown out a proposal to give same-sex couples the same tax perks as heterosexual couples after much debate.

The CDU's apparent change of heart was heavily criticized by the opposition Social Democrats, who accused it of being forced by the court into embracing reality.

The CDU has sought to boost its urban appeal ahead of a federal election in September by giving more prominent roles to women and ethnic minorities.

Long a staunch advocate of traditional family values, the party also faced some pressure from within to lure gay and lesbian voters, but that seemed a step too far for many at the congress last December.

The CDU's sister party in Bavaria, the Christian Social Union, warned against making any urgent changes.

"There is no grounds for taking hasty action or even making an about face on the subject of equal rights for married couples and same-sex couples," said Gerda Hasselfeldt, head of the CSU's parliamentary group in Berlin.

In Germany, homosexuals can form civil partnerships but are not allowed to marry. Opposition parties and gay activists accuse the chancellor's center-right government of dragging its feet on equality for gay couples. Civil partnerships are denied the tax privileges given to married couples.

Volker Beck, a lawmaker with the opposition Greens, warned in a statement on Sunday that opposition from the CSU and from some within the CDU suggested Merkel's government would be unable to push through legislation on its own.

He urged a free vote on the issue and said the Greens would help support a change in the law.

"If the CDU really wants to put an end to its discrimination of same-sex partnerships then we are ready to work together on this," Beck said.

(Reporting by Alexandra Hudson; Editing by Alison Williams)