The 1980s without Reagan

  Difficult to see Carter winning unless Reagan did something really stupid, possibly several times.  Possibly another Republican defeats him in the race for the party nomination or some accident/event means he won't/can't run would be the best option to achieve the OP.

  If you avoid Reagan the US economy is probably in a better condition as no tax cuts for the rich/big business leading to massive increases in the debts.  More and hence more expensive government than OTL but probably not greatly so and a slightly smaller military.  [Carter has pretty much the same increases in military spending as Reagan proposed].  However you probably wouldn't have the expensive Star Wars programme or quite as much gold-bricking of various military projects. 

  Still likely to see aid for the Afghan resistance, but possibly not the same support for the contras in Nicaragua or the payments to Iran.

  One big impact without Reagan is that a lot of research programmes may not be cut, especially in areas such as alternative energy.  Coupled with protection of nature reserves, most noticeably in Alaska but probably elsewhere as well.  As such your likely to see less oil produced in the US but more alternative sources coming into play.  This could advance the development of alternative energy systems by [rough guestimate] a decade or so compared to OTL.  Of course the big oil and gas companies, along with the coal ones and nuclear will fight such moves tooth and nail but they might have limited impact on the issue.  Given how much the US, along with Japan at the time, were the leaders for the west technologically this is likely to have a positive effect across the western world.  [Britain will still be a laggard because of the Thatcher regime.  However the high unemployment and rapid decline of the industrial base, along with the resulting social problems here could provide a deterrent to a revival of Reganism in 1984 or later.  Ideally in turn this would lead to a rejection of Thatcherism in Britain at some point rather than it continuing to dominate here. ]

  Not sure how much US international relations will change.  Suspect if the Falklands conflict still occurs the US will still support Britain and that you will see some build-up of NATO strength in response to the Soviet build up in the 1980s and a collapse of the latter.  [Hopefully as relatively quietly as OTL but there is of course the danger that butterflies could make it very nasty, both for the former Soviet empire and possibly the rest of the world.]  In turn with a reduced triumphalism in the US and a less strident right wing there you might see Russia trying the extreme free market route that caused so many problems in the 90s and help the rise of Putin.  This might mean Russia is a lot better off now.

  Anyway initial thoughts.