The move will achieve a “significant cost reduction” at a time when many trains are running empty or with few passengers, it said.
East coast operator LNER is to cut nine services from next week and Caledonian Sleeper will halt Aberdeen and Fort William services from tonight until Sunday December 6.
ScotRail services will be reduced in frequency on routes across its network from Sunday December 13.
It is understood these will be mainly at peak hours, which have seen the biggest fall in traveller numbers.
Some 272 trains a day will not operate, reducing the total to 81 per cent of normal from the current level of over 90 per cent.
However, extra carriages will be added where there is overcrowding to ensure social distancing.
Passenger totals remain down by 80 per cent of normal.
Peak hour commuting has sharply reduced as people work from home or on flexible hours.
Saturdays are now the operator’s busiest day of the week.
The Scottish Government has also asked people to minimise or avoid travel between different parts of Scotland, depending on which Covid level areas they are in.
ScotRail stressed there would be no change to staffing levels.
It also said the planned changes had not been finalised and were subject to change.
The reduction in services follows Scottish Government support for ScotRail being effectively doubled since the Covid outbreak with extra emergency payments running into hundreds of millions of pounds.
These have come on top of the operator’s normal annual subsidy of some £500 million – minister’s biggest single contract.
ScotRail operations director David Simpson told The Scotsman: “Throughout the pandemic, everyone across Scotland’s Railway [ScotRail and Network Rail] has worked tirelessly to deliver a robust and reliable timetable, with services across the country keeping key workers moving.
“We are currently in the process of looking at a revised timetable that allows us to continue delivering that reliable and vital rail service, but better reflects the reduced demand and changing nature of travel in Scotland and the need to ensure value for taxpayer money.
“The changes have still to be finalised and we will let customers know when that has happened.
"Our targeted approach will deliver more than enough seats to allow customers to travel safely.”
The Scottish Government’s Transport Scotland agency, which controls the ScotRail franchise, said ScotRail had been assessing its patronage to match services against demand, like operators across Britain.
A spokesperson for LNER said: “We have made some temporary changes to our timetable with effect from Monday November 16, which impact nine cross-border services.
“This is due to reductions in customer demand and to manage any staff shortages resulting from increased levels of self-isolation and clinically extremely vulnerable colleagues not being at work, in accordance with the latest restrictions.”
Caledonian Sleeper guest experience director Graham Kelly said: “We will continue to run a core service to support those guests who have essential travel requirements, while taking into account the welfare of guests, staff and industry partners.
"We look forward to welcoming our guests back on board in due course.”
Avanti West Coast, CrossCountry and TransPennine Express said they would not be reducing their cross-Border services.