Barack Obama has rewarded some of his most active campaign donors with plum jobs in foreign embassies, with the average amount raised by recent or imminent appointees soaring to $1.8m per post, according to a Guardian analysis.

The practice is hardly a new feature of US politics, but career diplomats in Washington are increasingly alarmed at how it has grown. One former ambassador described it as the selling of public office.

On Tuesday, Obama's chief money-raiser Matthew Barzun became the latest major donor to be nominated as an ambassador, when the White House put him forward as the next representative to the Court of St James's, a sought-after posting whose plush residence comes with a garden second only in size to that of Buckingham Palace.

As campaign finance chairman, Barzun helped raise $700m to fund President Obama's 2012 re-election campaign. More than $2.3m of this was raised personally by Barzun, pictured, according to party records leaked to the New York Times, even though he had only just finished a posting as ambassador to Sweden after contributing to Obama's first campaign.

Obama's chief money-raiser, Matthew Barzun. Photograph: Alamy

State Department veterans are increasingly concerned about the size of donations raised by political supporters who go on to take up top foreign postings. Thomas Pickering, who recently led the investigation into lethal attacks on the US embassy in Libya and represented the US at the United Nations, claimed the practice had become nothing more than "simony" – the selling of public office.

"All these people want to go to places where the lifestyle issues [are pleasant], and to some extent that produces this notion that life in these western European embassies is like Perle Mesta," he told the Guardian, referring to the "hostess with the mostest" who was ambassador to Luxembourg between 1949 and 1953 and who was known for her lavish parties.

"It has the effect of diminishing perhaps the sense that the US is treating these countries with the respect they deserve," Pickering said.

Susan Johnson, president of the American Foreign Service Association (AFSA), which represents career US diplomats, added: "The giving of ambassadorships to people who have raised a lot of money for the campaign has increased and that's a concern to us in particular.

"There was some thought that with Obama being such a 'change agent' that he might really do things differently – but it has just been a bigger let down."

Clutch of foreign appointments

Obama has made a clutch of foreign appointments recently. The 16th century Villa Taverna in Rome has just gone to John Phillips, a Washington lawyer who raised at least $500,000. John Emerson, a Los Angeles fund manger, will get to meet future contacts as ambassador to Germany after he raised $1.5m. Jane Stetson, heiress to the IBM fortune, is tipped as frontrunner for Paris after she raised $2.4m for Obama.

In total, nine sought-after postings in Europe, the Caribbean or Asia have been given to major donors in recent weeks, with a further three in France, Switzerland and Hungary earmarked to come soon. Of these 12, the precise bundling data is available for 10. According to a Guardian analysis, using the figures leaked to the New York Times, the average amount raised by each donor is $1.79m.

Official campaign finance records give only minimum figures for how much each donor raised among friends and family (a process known as bundling). Even using the published 'minimum' donations declared for these bundlers, the amount raised by donors rewarded with foreign postings has soared. The appointees to those same 10 embassies raised at least $5m in 2013, compared to a minimum of $3.3m in 2009, at least $1.3m under George W Bush in 2005 and at least $800,000 for Bush donors in 2001.

Many of the capitals have grown resigned to the process. "All that really matters is that the ambassador is close to the White House – and his top fundraiser usually is," said one British diplomat, speaking anonymously about Barzun's appointment.

But to State Department veterans, the notion that only fundraisers can get messages through the West Wing is even more alarming. "To some extent, this question of having the ear of the president, and who has it, shows the seriousness of the issue," said Ambassador Pickering.

Johnson, the AFSA president, said many donors have less political influence than their host countries like to imagine. "Some foreign countries like the idea that they are getting a friend of the president, but our experience has been that genuine friends are pretty small; most of these people are friends of friends; and they don't get to call the president right away," she said.

"In a few exceptional cases they are not detracting from credibility of diplomatic service, but at the scale it's being done it is undermining the concept of a career diplomatic service and weakening the strength and capacity of the diplomatic service."

Johnson estimates the percentage of ambassador posts given to political appointees rather than career diplomats has remained roughly steady under Obama at around 30%, but most of these are in parts of the world unattractive to wealthy donors. The share taken by political appointees in western Europe and wealthier Asian capitals has reached between 70% and 85%, the AFSA estimates.

One factor cited by defenders of the practice is that private means are needed to fund the lifestyle led by ambassadors, but the importance of this is disputed by State Department veterans.

"In the embassies I've been in, normally you have a representation budget," said Johnson. "Whether we skimp on it in places like London and Paris and these people add to it so they can serve the best champagne and canapes I don't know, but I don't think it's necessary to be wildly wealthy any more."

She also said many are disappointed by the reality of embassy life. "If the dog ruins the furniture, you have to pay for it. It's like being a guest in someone's house."

Dysfunctional leadership

This can cause problems of its own. A report by the State Department inspector general into a crisis at the embassy in the Bahamas found that Obama campaign finance chair Nicole Avant presided over "an extended period of dysfunctional leadership and mismanagement, which has caused problems throughout the embassy". Prior to her appointment as ambassador, Avant was vice president of Interior Music Publishing and was absent from the embassy 276 days between September 2009 and November 2011, according to the report. In response to the report Avant said she "had inherited a dysfunctional embassy".

Another official report into the Obama campaign donor appointed to Luxembourg, Cynthia Stroum, found she had been "aggressive, bullying, hostile and intimidating" and left her embassy in a "state of dysfunction". Stroum resigned after the report.

State Department veterans say motivations vary among political donors. "Some go to pleasant islands where the climate and residence are delightful, others just want the title, like British people lust after peerages," said AFSA's Johnson. "People think: gee, I really want to call myself ambassador, so I can go buy myself one. Others are perceived to want to just meet people, broaden their contacts of future business contacts people who can help them in their day job."

The White House insists all its ambassadors are well qualified, regardless of their campaign history. "I am proud that such experienced and committed individuals have agreed to serve the American people in these important roles," said Obama in a statement issued with Barzun's appointment.

The Foreign Service Act of 1980, states that "contributions to political campaigns should not be a factor in the appointment of an individual as a chief of mission."

At at time when the US is reaching the limits of its "hard power", career foreign service staff argue it is time for professional diplomacy to mount a comeback.

"We tried a lot of military stuff and have we come to the realisation that not every problem out there can be solved by troops, no-fly zones and drones," concludes Johnson.

"Diplomacy and managing the inter-relationships between countries is actually important, and we ought to be taking it more seriously, preparing people for it and seeing it as a long-term career – not as just something you do for a few years while you are preparing to do something else."