UPDATE 1-Former Swiss banker pleads guilty in U.S. tax probe

* Ex-banker Christos Bagios sentenced to time served

* Change of plea was expected, judge notes his help in probe

* Long-running probe pressures Swiss on banking secrecy

WEST PALM BEACH, Fla., Nov 6 (Reuters) - A former Swiss banker pleaded guilty on Tuesday to helping Americans hide millions of dollars from U.S. tax authorities, and a judge noted the banker has aided investigators in a broad U.S. probe of tax evasion that has put Swiss banks on the defensive.

Christos Bagios, formerly employed by Swiss financial giants UBS AG and Credit Suisse Group AG, changed his earlier plea from not guilty in the U.S. District Court for Southern Florida. The change of plea had been expected.

A Greek citizen and Swiss resident, Bagios was sentenced by Judge Kenneth Marra to time already served, including 37 days in prison and nearly 19 months under house arrest in Miami.

In a sign that Swiss banks may come under further pressure, the judge cited the former banker's ``substantial'' assistance in a broad federal probe by the U.S. Department of Justice of Swiss and Swiss-style banks.

Matthew Menchel, a lawyer for Bagios, described his client as ``relieved.''

Bagios, 47, worked at UBS from 1999 to 2005. He was a senior banker at Credit Suisse when he was arrested in New York in January 2011. He was later charged with helping 150 Americans hide up to $500 million during his time at UBS.

Switzerland's long tradition of banking secrecy has been under pressure for some time from the United States and other countries. Burdened by deficits and debt, many countries are trying to collect more taxes from well-to-do citizens.

A broad inquiry by U.S. authorities into tax evasion services rendered to Americans by Swiss financial institutions has been under way for years. At least 11 banks are under investigation, and dozens of Swiss bankers and American clients have been indicted on tax evasion charges.

Last month, Bagios pleaded not guilty. But at the same time, he arranged for a change-of-plea hearing, leading some tax lawyers tracking his case to speculate that he was cooperating with U.S. officials in the probe of Swiss banks.

Bagios had faced up to five years in prison as well as a $250,000 fine.

Credit Suisse, Switzerland's second-largest bank, disclosed last year it was being investigated by the Justice Department. The investigation intensified after UBS, the largest Swiss bank, paid $780 million to settle charges by the U.S. government.

Other banks under investigation include Zurich-based Julius Baer and some Swiss cantonal, or regional, banks along with UK-based HSBC Holdings and three Israeli banks, Hapoalim, Mizrahi-Tefahot Bank Ltd and Bank Leumi . In February, Wegelin, Switzerland's oldest private bank, was indicted.