The US Government was a large cog in the coalition of state’s that attempted to sharpen the thorn in the side of the Vietnamese that was represented by the remains of the Khmer Rouge. The role of China is very important here, and naturally the overall context of the latter stages of the Cold War.

The ’support’ that the US provided the group exiled on the border of Thailand and Cambodia was primarily financial, and also worked through the State Department’s active discouragement of any countries or the world bank providing loans or financial support to Vietnam or the Peoples Republic of Kampuchea. The Vietnamese economy was strangled in order to pile on the pressure on an already weakened system. Aside from these financial measures, the political manoeuvres taken to keep the Vietnamese invasion of Cambodia as the only problem worth talking about. This stymied any real efforts to recognise the Khmer Rouge as a group that needed to be stopped and brought to justice. Efforts that while eventually acted upon have suffered from the time it took to do so.

To answer your question more directly, as it seems you are generally aware of the context around this situation, would be to say yes, there is a consensus that the US did support the Khmer Rouge, and the reasons for this (Vietnam War/Relations with China) are quite clear.

The extent, to my knowledge, is mostly financial but was provided with certain caveats or in often clandestine ways. Most military funding and armaments were provided by China to their Cambodian ally. As you’ve noted, Pilger is one of the journalists that has spent a lot of time digging around this issue and blaming the ‘imperialists’ as much as he would like to. I like his work generally but his bias can be a little on the nose sometimes. He gives the figure of around 85 million dollars which he found from a government source, I’ve not seen that particularly disputed, however the aid was ostensibly not for military uses… but if you are providing aid in order to keep one side of a civil war in action then it is hard to disentangle that money. The last chapter of Elizabeth Becker’s ‘When the War Was Over’ deals with the political situation post ’79, as does Fawthrop and Jarvis’ ‘Getting Away with Genocide?’ but these more or less deal with themes you might already be aware of, namely political and financial support for the Khmer Rouge as part of a US/Chinese political agenda.

Theres that great quote which always gets put out around this subject and you’ve probably no doubt heard it but the acknowledgement of the US about the kind of muck they were dealing in is pretty damning. This of course is Robert Rosenstock’s admission that after Ieng Sary came to shake his hand following the vote to keep the Khmer Rouge in their seat at the UN, the diplomat said that he ‘felt like washing his hands’.