The Health and Safety Executive said the mile-long bridge - which carries 1,000 trains a week over the river Forth - was still safe, but Railtrack needed to repair existing damage and step up maintenance procedures.
The assessment by the HSE was prompted by public concern about the condition of the bridge which has recently been shedding large flakes of red paint.
The report said: "The bridge is over 100 years old and some deterioration in its condition is to be expected. However, the assessment has indicated that over many years the maintenance system has not been robust enough to prevent significant deterioration in certain areas of the bridge."
Engineers from HM Railway Inspectorate carried out a survey of the condition of the bridge - a hazard analysis and structural study. In their judgement the bridge was safe in its current condition to carry Railtrack's present loading.
Although the bridge has been allowed to deteriorate, its structural integrity was not compromised. Its carrying capacity in its present condition complied with modern standards of safe design for bridges. The existing maintenance regime needed improvement if deterioration was to be stopped and potential structural problems in the future were to be avoided, the study said.
Sam Robertson, chief inspecting officer of railways, said he was not alarmed by the survey, but added: "We were dissatisfied, disappointed, concerned to find that parts of the bridge had been allowed to deteriorate with no apparent maintenance over long periods and this was confirmed because of a complete lack of records."
He explained that when Railtrack took responsibility for the bridge two years ago they found big gaps in maintenance records.
"Clearly it indicates a lack of care on the part of people responsible at the time."
Railtrack now has to meet several requirements including completing an overall survey of the bridge's condition, and establishing a full understanding of how the bridge and in particular its bearings - which allow contraction and expansion - were designed to work.
It will also have to complete a structural assessment of the bridge and prepare an action plan for restoration and repairs. Railtrack will also have to prepare a maintenance plan to cover the future upkeep and monitoring of the bridge's condition.
Mr Robertson said that the HSE had given Railtrack formal notice of its intention to issue improvement notices in respect of these items.
The report said some secondary sections, steel angle straps, were so rusted they were broken through and had to be replaced. Some parts of the bridge had no paint or coating other than the oil treatment applied when it was built. "A significant backlog of painting work needs to be addressed." Between 50 per cent and 70 per cent of the bridge required some sort of coating.
The survey showed the paint applied over the last 100 years was no longer providing adequate protection to the steel underneath. "In recent years, grit-blasting had been used to remove old paint, but this had also removed the original oil and coating from the steel which gave a degree of protection.
Railtrack said it would be spending more than pounds 3m on the bridge in the next financial year. A spokesman said: "We too have carried out an in- depth analysis on the carrying capacity and condition of the bridge and we are preparing a maintenance plan which will preserve the bridge indefinitely."
The statement added: "Railtrack welcomes the Health and Safety Executive's report and its acknowledgment that the Forth Bridge is safe, its integrity is not compromised and that it complies with modern standards of safe design."Reuse content