UPDATE 1-Top banks reduce capital shortfall to $20 bln - BIS

* Capital shortfall 15 bln euros vs 58 bln 6 months ago

* Top 102 banks' core capital improves to 10.2 pct avg

* Capital gap down by more than 350 bln euros over 3 yrs (Adds details of capital, shortfalls, previous estimates)

By Steve Slater

LONDON, Sept 11 (Reuters) - The world's top banks havealmost eliminated the shortfall in capital they would have ifnew regulations that are being phased in were in full forcealready.

The Bank for International Settlements (BIS) said onThursday the world's top 102 banks would have been 15.1 billioneuro ($19.5 billion) short of capital to reach a 7 percenttarget for common equity at the end of December, compared withan estimated shortfall of 57.5 billion euros six months earlier.

This continues a sharp reduction in the theoretical capitalshortfall faced by banks, which was estimated at 374 billioneuros less than three years ago.

The gap has narrowed as banks have raised equity, held backmore of their earnings, shed loans and other assets andrestructured their businesses.

The BIS has been monitoring how well banks are transitioningto the implementation of tougher capital rules, which are beingphased in from 2013 to 2019, and releases its findings every sixmonths.

The banks in the sample made after-tax profits of 419billion euros prior to dividend payouts in 2013, BIS said.

Most of the capital shortfall would be at European banks.

Europe's top 42 banks would have been 11.6 billion euroshort of capital to reach the 7 percent target (which includesadd-ons that are applied for the biggest banks), down from a36.3 billion shortfall six months earlier, the European BankingAuthority said.

The BIS said the common equity capital ratio, a measure ofcapital strength, of the top global banks averaged 10.2 percentof risk-weighted assets at the end of December, up from 9.5percent at the end of June 2013.

It said the average leverage ratio - a simple measure ofequity to assets, without accounting for the riskiness of loans- was 5 percent for the 102 banks, but nine of the firms did notmeet the minimum leverage ratio requirement of 3 percent.

($1 = 0.7735 Euros) (Reporting by Steve Slater; Editing by Nishant Kumar and MarkPotter)