They have far fewer powers than constables, and critics have claimed they lack the training to do an effective job.
The Met cuts will also see a scaling-back of the force's murder squads after homicide rates across the country fell to their lowest level since 1983 in the latest crime figures.
The force has 24 murder investigation teams, each led by a detective chief inspector with 27 other detectives and seven civilians.
The source said the teams would be cut "significantly" from current levels of about 670 and will be redeployed to work with Safer Neighbourhood Teams, which handle lower-level crime in the community.
More police stations are also likely to close and the number of chief superintendents slashed to cut the management wage bill.
Bernard Hogan-Howe, the Met Commissioner, said last month that there was a question mark over the future of a 28-strong team within the Met's Homicide and Serious Crime Command which has been re-examining evidence in the disappearance of Madeleine McCann in Portugal five years ago.
Boris Johnson, the Mayor of London, and his City Hall officials have the final say on the Met's budget.
A source close to the discussions said: "The murder teams are very over-staffed but they are ring-fenced and this needs to be addressed. As the murder rate has fallen we've got murder detectives with less and less to do.
"We're not talking about getting rid of expert detectives, but redeploying them to investigate lesser crimes such as assaults and burglaries.
"This will involve quite big numbers. To make this work it will have to be quite a radical redeployment of resources - we're not just talking about five or ten per cent here and there.
"We are also going to have to lose hundreds of PCSOs, though the final figure won't be clear until February."
It is understood that officials at the office of London Mayor are determined to force through cuts which will be unpopular with rank-and-file officers.
The Met is by far the largest police force in the country, with 32,000 officers, and provincial forces tend to follow its lead in terms of structures and procedures.
The force's final budget will be drawn up by Met Commissioner Bernard Hogan-Howe in conjunction with Stephen Greenhalgh, Mr Johnson's deputy mayor for policing and crime, by February and voted on by the London Assembly.
In July the former HM Chief Inspector of Constabulary, Sir Denis O'Connor, warned the Met has to find another £233 million of savings by 2015 to balance its books on top of the existing £537 million cuts.
Earlier this year The Sunday Telegraph reported how Scotland Yard, senior Home Office officials and representatives of the Royal household are due to embark on an inquiry into Royal Security, which could lead to "non-working" members of the Royal family losing their armed guards.
Due to commence next month, it will be the third time protection arrangements for the Royal family have been scrutinised in less than three years, reflecting Scotland Yard's desire to cut costs.
