Serious concern has been raised about the capacity of public health doctors to deliver on government policies to improve health.
Public health doctors co-ordinate policy
A Faculty of Public Health report highlighted fears about job losses, and cuts to training budgets.
It found that only 36% of Primary Care Trusts in England felt they had the capacity to deliver effective services.
The government said specialist numbers had remained steady, and stressed public health was a top priority.
Public health doctors specialise in developing strategies to improve the health of the population, overseeing local health promotion initiatives, and co-ordinating responses to outbreaks of disease.
The FPH report warned the restructuring of PCTs and Strategic Health Authorities could result in 100 to 150 senior positions being lost.
The survey also revealed a 40% reduction in planned recruitment for public health training for 2006, compared with 2005.
The FPH has been told that four of the 13 regions plan to cancel their public health training completely for this year.
This, experts warn, could lead to a long-term shortage of public health specialists.
The survey also found that 18% of public health consultants were considering leaving the specialty within the next five years.
The FPH has written to public health minister Caroline Flint, asking her to tackle the problem.
Professor Rod Griffiths, FPH president, said the government had demonstrated a commitment to public health in the White Paper Choosing Health.
But he said: "There has not been the investment there needs to be in public health, and there has not been the dramatic rise in numbers of consultants we have seen in other specialties.
"And with every NHS reorganisation, significant damage is done to the public health workforce.
"Without an adequate, appropriately trained, public health workforce the public's health will be put at risk.
"Steps must be taken to ensure that public health capacity is protected."
Chris Lovitt, chair of the FPH's Trainee Members Committee said: "This report underlines the need for an expansion in the number of trainees recruited.
"The planned massive cuts in recruitment numbers must be reversed if the future of public health is to be secured."
Dr Justin Varney, of the British Medical Association's Public Health Committee, said it was "recklessly short-sighted" to squeeze public health training.
"It is the very specialty which must expand to tackle the health gap between the best and worst off."
Dr Fiona Adshead, the Deputy Chief Medical Officer, said public health was a top priority for the government.
She disputed the claim there had been a significant reduction in capacity, and said government figures showed there were 718 specialists in 2000, and 788 in 2004.
Dr Adshead said the government had written to NHS organisations to highlight the importance of public health, and would work closely with strategic health authorities to ensure the specialism was given due priority.
"We also wrote to SHA finance directors to make clear that PCT financial targets should exclude all consultant and specialist public health posts."
However, she accepted more needed to be done to increase training capacity.