Historic Scotland, which maintains 345 well-known landmarks including castles, abbeys, monuments and museums have identified 1,700 “urgent” conservation issues.
The report, which had not been shown to MSPs, warned repairs to buildings involving scaffolding may not be possible due to the cost.
Investment in infrastructure has been “inadequate” and Edinburgh and Stirling castles have “management issues”, the document concluded.
The study predicted £42 million will be needed over the next 20 years to conserve historic buildings, with a further £63 million required for new states.
Another £67 million is needed for visitor presentation and tourism, bringing the total to £172.7 million, a figure the report said is “over and above” current budgets.
Among the thousands of conservation issues flagged up by the report were 7,500 marked of “medium” importance and 1,700 deemed to be “urgent”.
The document emerged two weeks after the Scottish Government set out plans to merge Historic Scotland with the Royal Commission on the Ancient and Historical Monuments of Scotland (RCAHMS).
However, Fiona Hyslop, the Scottish Culture Minister, made no mention in her parliamentary statement of the report, which was written in February by two senior Historic Scotland officials.
Liz Smith, the Scottish Tory culture spokesman, said she would write urgently to Ms Hyslop, adding: “This is a deeply worrying state of affairs.”
“This raises concerns about the future maintenance of our historic environment and what criteria will be used if certain projects have to take precedence over others.”
According to the report: “Lack of project funding means that it is increasingly likely they will be generally limited to ground-level works (ie those not requiring scaffolding).”
If more funds are not made available, the document warned there would be a “loss of historic fabric and leave Historic Scotland exposed to accusations of having different standards for its own properties compared to the other 7,700 Ancient Monuments” not cared for by the agency.
The document was written by David Mitchell, its director of conservation, and Stephen Duncan, its tourism director.
David Mitchell and tourism director Stephen Duncan compiled a report on the state of the heritage sector in February.
A spokesperson for Historic Scotland said: “The Government recognises the scale of the challenge across the agency’s sites and commissioned this report to get a fuller understanding of the key priorities. This work is ongoing.”