Over the last two years, the number of people living within a 440-yard walk of a bus stop with regular services has declined from 44% to 41% over, Strathclyde Partnership for Transport has found.
Between 2009 and 2011, those living in the 15% most deprived areas saw access to bus stops with four or more services fall from 60% of the population to 45%.
Semi-rural areas also suffered higher-than- average cuts, with only 42% of people near a bus stop with at least one bus an hour in 2011, against 48% two years ago.
The results do not include remote rural areas, where services are scarcer.
The findings have prompted concern that poor communities affected by high levels of unemployment are now suffering a double whammy as they lack the transport links needed to ensure people have access to jobs.
Jonathan Findlay, chairman of SPT, said the council-run transport organisation had limited funds to subsidise "socially necessary" bus services that were withdrawn by commercial operators.
He said: "This is a growing trend affecting all of Scotland and highlights a more fundamental issue of dealing with a deregulated bus industry.
"We would love to do more to increase services, but there is not enough money to do so."
Despite buses in Scotland providing 467million passenger journeys in 2009 – more than six times more than trains – the industry receives a fraction of the support given to the rail network, whose funding is protected until the next five-year spending cycle in 2014.
Last month's budget saw annual rail funding of £700million maintained, but saw support for bus services, including the Bus Service Operators' Grant (BSOG), cut to £54m – 19% down on a deal struck a year ago between the Scottish Government and bus industry.
Funding for Scotland's free bus travel scheme is due to be frozen at £192m for two years following a £7m increase next year.
The SPT survey also appeared to confirm that poor communities, where car ownership is lower and access to rail services tends also to be lower, are far more dependent on buses.
A spokesman for CPT said some of the SPT findings could be driven by relatively small changes to service frequencies, such as a bus operating every 12 minutes instead of every 10.
He added: "It is fair to say the impact of the recession, increasing operating costs, reductions to the reimbursement rate for concessionary journeys and cuts to the Bus Service Operators' Grant budget may mean operators have to consider service frequencies and fares.
"However, the SPT monitoring statistics are not conclusive proof that service cuts are necessarily prevalent in the Strathclyde area."
A spokesman for Transport Scotland, the Government agency responsible for bus services, said the SPT research showed the drop in services had been driven by a downturn in demand rather than Government funding.
He said: "Over the last few years overall bus funding has been maintained and this will continue over the spending review period, despite the challenges of real-terms Westminster cuts to Scotland's budget."
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