CANBERRA, Australia — President Obama announced Wednesday that the United States planned to deploy 2,500 Marines in Australia to shore up alliances in Asia, but the move prompted a sharp response from Beijing, which accused Mr. Obama of escalating military tensions in the region.

The agreement with Australia amounts to the first long-term expansion of the American military’s presence in the Pacific since the end of the Vietnam War. It comes despite budget cuts facing the Pentagon and an increasingly worried reaction from Chinese leaders, who have argued that the United States is seeking to encircle China militarily and economically.

“It may not be quite appropriate to intensify and expand military alliances and may not be in the interest of countries within this region,” Liu Weimin, a Foreign Ministry spokesman, said in response to the announcement by Mr. Obama and Prime Minister Julia Gillard of Australia.

In an address to the Australian Parliament on Thursday morning, Mr. Obama said he had “made a deliberate and strategic decision — as a Pacific nation, the United States will play a larger and long-term role in shaping this region and its future.”