Reiterating his manifesto promise, Johnson said that funding of £16.5m for an extra 440 police community support officers to patrol buses and Tube stations will come from cutting Transport for London's advertising budget.
He has also promised to mount an inquiry into bureaucratic waste at City Hall, which is expected to lead to 14 jobs being cut in the mayor's 70-strong publicity and marketing team.
Johnson said that there were many talented workers at City Hall but added that he had been elected to ensure that Londoners saw "taxpayer value".
The cuts in adspend will mean less high profile campaigns such as the Metropolitan Police's Operation Trident campaign, created by Miles Calcraft Briginshaw Duffy, to fight gun crime.
The Conservative Party has previously criticised the excessive use of public spending on such campaigns.
During a visit to Dagenham Fire Station yesterday, Johnson declared that crime would be his major focus. He said that crime is a "huge concern" for Londoners and that he would work "night and day" to make the capital safer.
There is no indication that the move will start any agency reviews. The roster agencies for the Greater London Authority include WCRS, Farm Communications and Spirit Advertising, while MCBD holds the account for the Met Police.