North Yorkshire Police said the two members of Harrogate's Neighbourhood Policing Team visited the McDonald's in Cambridge Street on April 1 following reports that a group of teenagers banned from the restaurant had entered.
They had been given a dispersal order by police following anti-social behaviour earlier in the evening.
But when the group refused the leave after being asked to do so by the PSCOs, police said an "altercation" took place leaving them injured.
A statement from the force said one was left with a suspected broken nose and the other suffered "tissue damage to the cheek".
"Both currently remain in hospital for treatment and appropriate support has been put in place with regard to their welfare," it added.
Three girls, aged 13, 14 and 15, have been arrested.
Inspector Phoebe Southall said: "No one deserves to go to work and be assaulted, especially as they work to protect the public and keep our communities safe. It is not just ‘part of the job’ and we will investigate any incidents of violence towards our staff thoroughly.
“We would urge anyone who either witnessed the attack or has any information or mobile phone footage that may have captured something to please get in touch.”
Anyone with information or mobile phone footage is asked to email [email protected] or call North Yorkshire Police on 101, quoting incident number 12220055279. Alternatively, contact Crimestoppers anonymously on 0800 555 111.