LONDON — Given red-carpet treatment in London, Chancellor Angela Merkel of Germany responded Thursday with warm words but few hard promises to Prime Minister David Cameron, who is counting on her support in his efforts to loosen British ties to the European Union.

Ms. Merkel became the first German chancellor to address both houses of Parliament since 1970, lunched at 10 Downing Street, then took afternoon tea with Queen Elizabeth II — an itinerary that underlined the importance Mr. Cameron attaches to the leader of the biggest European Union nation. By contrast the French president, François Hollande, was received recently at a military air base then taken to a country pub by Mr. Cameron for lunch.

In return for her top-notch treatment, Ms. Merkel offered warm praise for Britain’s historical contribution to Europe, and she joined cause with Mr. Cameron in calling for curbs on welfare entitlements for migrants crossing European Union frontiers. There should be freedom of movement for workers but not migration “into social security systems,” she told a news conference.

Yet, while keeping open the prospect of reforms to the 28-nation European Union, she pointedly declined to support Mr. Cameron’s efforts to rewrite the bloc’s founding treaties, a process that he believes will help him reshape British relations with Brussels.