TOKYO, Jan 19 (Reuters) - Japanese government bonds were steady to slightly firmer on Tuesday, with solid demand at a 20-year bond auction allaying fears that the Bank of Japan could widen its policy target in March. The 20-year bonds were 3.35 times oversubscribed at the auction held by the Ministry of Finance on Tuesday, with an average bid of 0.443%. The 10-year JGB yield was flat at 0.045%, while the 20-year JGB yield was also flat at 0.440%. The 30-year JGB yield fell 0.5 basis point to 0.650%, off two-year high of 0.675% touched on Monday. The two-year JGB yield was flat at minus 0.130%. (Reporting by the Tokyo markets team; Editing by Shailesh Kuber)