Bismillah..
.hgt is SRTM data extension. you can directly export this kind of data to .dem (USGS) from Global Mapper (registered only)
1. just click File – Export Raster and Elevation Data – Export DEM – OK

Export .hgt to.dem in GM
after that just load your ArcView
2. move your cursor to File – Import Data Source – Select USGS DEM – OK

Import .dem in ArcView
3. then create contour from Surface – create contour – insert your interval kontur needed..

Create contour
4. final step is convert to shapefile, just move your cursor to Theme – Convert to shapefile..choose where you want to save your .shp (complete with tabular data).

Convert to .shp

choose place to save your data

Well done, now you just have your contour complete with it's tabular data
after all steps, you could modifies your data..
good luck yooo..:)
Note:
a. In step 4. make sure your “contour” in active position..select it for activated
the image must in stereo format like SPOT5 HRS (High Resolution Stereo) or like TerraSAR.. or aerialphotogrammetry, which every single imagery could produced contour with photogrammetry processing (3D glasses)..