I am not at all sure what sending a US force to Singapore would do for the US.
Even for the British. The US had a base in the Philippines. It is around 720-750 miles from Manila to Hong Kong. It is over 1600 miles from Singapore to Hong Kong.
Japanese have to pass by the Philippines to get to SE Asia or the Dutch East Indies.
The US was prohibited by treaty from strengthening the Manila defenses from 1922-23 until 1936.
The politics of putting more forces (money) into the Philippines in 1930s when there was a movement to make the Philippines independent is subject to question but with the Philippines heading for independence the US interests in the whole area gets smaller.
PI independence
The intention was to move towards full independence during the period 1935 to 1946, with gradual changes to the PI Constitution during that period. But would a US Govt really have been prepared to simply abandon the PI even after full independence with a rampant Japan still in place?
Naval facilities
Cavite naval base, the main USN facility in the PI for its Asiatic Fleet, could support nothing larger than a cruiser, and it proved no deterrence.
For that reason, the furthest West in the Pacific that the US could base its main force of battleships and carriers was PH. Still 4,800 miles away from the scene of any likely action. And it had virtually no fleet train in 1940/41 that would allow it to swiftly cross that ocean to intervene in any action by the Japanese.
Singapore
The RN dockyard there had the facilities to support a significant fleet. The largest dry dock in the world at the time IIRC. The 3rd largest floating dry dock in the world, AFD.IX capable of lifting vessels of 50,000 tons. Plus another smaller AFD. Massive oil storage facilities. Plenty of store sheds for naval stores.
Those are the kinds of facilities that the battleships and carriers of the US Pacific Fleet needed in the western part of the Pacific region if it was to be a serious deterrent to Japanese expansion southwestward.
Inter war Singapore was chosen as the main fleet base location for the RN because Hong Kong was seen as too exposed and the developed parts of Australia (on the east coast) were too far away. Darwin had zero to commend it in those days, other than a large stretch of water, and was virtually unconnected to civilisation! The battle against the IJN was expected to occur initially around Formosa/ Taiwan, to be followed by an advance to blockade Japan, probably seizing an advance base near Okinawa.
If the policy really was to be one of deterrence then the threat to Japan had to be credible. A sizeable fleet, USN or RN at Singapore might have been seen as a bigger threat to their ambitions than a USN fleet sitting at PH virtually able to go anywhere. Cavite could then have acted as a refuelling / restoring station for any TF deployed northwards.
As part of a deterrence strategy it has some merit. The downside of course is that it would leave the defences of the US West Coast vulnerable. But how much if a concern was that? It was a major operation to get the KB to PH logistically. Would it ever have been able to reach the West Coast? Such a move leaves Japan itself vulnerable to attack from the fleet at Singapore.
We know how the US did balance the risks. FDR moved the fleet base forward to PH. It proved to be no deterrent.