* Barroso joined bank two years after leaving EU executive
* Watchdog says Juncker failed to probe predecessor properly
* Row resurfaces as Juncker faces own questions (Recasts with Barroso response, letters, other probes)
BRUSSELS, March 15 (Reuters) - Former European Commission president Jose Manuel Barroso denied on Thursday he had lobbied ex-colleagues for his new employer Goldman Sachs, hitting back at what he has called a personal "political attack" by the EU's ethics watchdog.
"I have not and will not lobby EU officials," he tweeted after a European Ombudsman's report said his successor at the Commission, Jean-Claude Juncker, had failed to properly scrutinise whether Barroso's new job undermined fragile public trust in the European Union.
Barroso, a former Portuguese prime minister, ran into furious criticism, including from Juncker, when he joined the U.S. bank in July 2016, less than two years after leaving an EU executive that eurosceptics branded out of touch with voters.
Brussels was reeling at that time from Britons' vote to quit the bloc just two weeks earlier.
The controversy has resurfaced as Juncker faces his own troubles. The European Parliament and the Ombudsman are reviewing complaints after last month's surprise promotion of his chief-of-staff to run the Commission's civil service.
Barroso said Ombudsman Emily O'Reilly made no "legal assessment" of his duties for the bank but said he did not oppose her call for a new review by the Commission's ethics committee which in 2016 found no reason to object to his job.
In an exchange of letters with O'Reilly, published by the Ombudsman on Thursday, Barroso accused her of mounting a "thinly veiled ad personam political attack".
O'Reilly in turn dismissed Barroso's account that his meeting in October with former Commission colleague Jyrki Katainen was a private matter. She said Katainen, now a vice president under Juncker, had registered it in the EU public lobbying record as a meeting with "Goldman Sachs".
In light of that meeting, O'Reilly recommended the Commission's watchdog determine whether his new employment met the obligation for former commissioners to act with integrity and not damage the EU's image. The panel can cut pension rights for any breach, but has never done so.
"Much of the recent negative sentiment around this issue could have been avoided if the Commission had at the time taken a formal decision on Mr Barroso's employment with Goldman Sachs," O'Reilly said in a statement. It could have obliged him not to engage in any lobbying at the Commission, she added.
Despite vocal criticism, others have defended the right of top officials to find new work and have said attacking banks, and Goldman Sachs in particular, showed political prejudice.
Goldman Sachs said in a statement that Barroso, who left his position as president of the Commission in late 2014, had "from the beginning of his time with us recused himself from representing the firm in any interactions with EU officials".
Juncker had criticised Barroso for taking a job with a bank accused by some of contributing to Europe's economic crisis but said he could not obstruct the move as an 18-month "cooling off" period to avert conflicts of interest had lapsed.
Juncker later doubled the cooling off period for himself and successors and asked the ethics committee to look at Barroso's move. The watchdog found no ground to object in late 2016 but the Ombudsman launched her own inquiry last year.
A Commission spokesman said it would consider her report and reply within her three-month deadline. Noting Juncker's changes to the code of conduct, he said. "We have very strict and very comprehensive requirements." (Additional reporting by Sinead Cruise in London Editing by Edmund Blair)