Oct 9 (Reuters) - The Czech Republic's gross central government debt rose to 746.3 billion czech crowns ($33.35 billion) at the end of September from 728.9 billion crowns at the end of June, the Finance Ministry said on Monday. GOVERNMENT DEBT SEPT 06 JUNE 06 MARCH 06 SEPT 05 (CZK bln) total 746.3 728.9 698.2 662.6 average maturity (in years) 5.9 6.1 6.2 5.9 marketable debt 711.3 696.1 667.4 633.5 modified duration (in years) 3.8 3.7 3.8 4.0 NOTE. Data show levels as of the end of the period listed. The modified duration figure stands for marketable debt only and includes the Finance Ministry's interest rate swap transactions. Average maturity was within the ministry's target of 6.0-7.0 years. (Reporting by Mirka Krufova in Prague) ((For past economic data and analysts' forecasts, double click on <CZ/ECON01>)) ((Editing by Alan Crosby; prague.newsroom@reuters.com; Reuters Messaging: mirka.krufova.reuters.com@reuters.net; +420 224 190 477)) ($1=22.38 Czech Crown) Keywords: ECONOMY CZECH DEBT TABLE