Singapore has agreed "in principle" to the US request "to forward deploy up to four littoral combat ships (LCS) to Singapore on a rotational basis," the two sides said in a joint statement.
Final details of the agreement will be worked out by naval leaders from both countries, said the statement issued after a meeting in Singapore between US Defense Secretary Leon Panetta and his Singaporean counterpart Ng Eng Hen.
Singapore, located along the crucial Malacca Strait that links the Indian and Pacific Oceans, had previously agreed to at least two of the US littoral combat ships deploying.
US officials cite the deal on the littoral combat ships, a speedy new class of vessel, as the latest example of Washington's strategic shift to the Asia-Pacific.
Panetta, on a nine-day tour of Asia, said on Friday the US military's focus on Asia will rely on rotating deployments of troops and ships instead of large-scale, permanent bases.
In an apparent bid to pre-empt possible opposition to the agreement, the joint statement made a point of underlining that the ships will not be permanently stationed in Singapore and the crews will stay aboard their vessels.
"The LCS will not be based or homeported in Singapore, and the LCS crew will live on board the LCS for the duration of their deployment," the joint statement said.
By avoiding permanent bases, the United States hopes to secure a military presence in key areas without incurring the high costs of large-scale outposts and risking political backlash against American forces in partner countries.
A senior US defence official played down the rules for the ship crews.
"Sailors live aboard ships everywhere. That's the case on deployed ships around the world. This isn't some kind of special or particular arrangement with Singapore," the official said.