Nikkor 35mm or Nikkor 50 mm 1.8 (Nikon D3100)?

Which lens between these two (Nikkor 35mm or Nikkor 50 mm 1.8) are worth for portrait? I will soon buy a Nikon D3100 and I would like to have an additional lens which is not expensive but good for portrait.

The 50mm would be better.

The 50mm 1.8 will not auto focus on the D3100. You would have to go with the 50mm 1.4 which is equivalent to 75mm on the crop sensor. The 35mm would be equal to 52.5mm which is a normal focal length. The 50mm 1.4 would be better for portraits but both would work fine.

I'd get the 35mm, because it auto focuses, gives great quality pictures, and is only $199 at Best Buy. Only the AF-s line of Nikon lenses auto focuses with the camera because they have an in-lens auto focus motor, and the Nikon DSLR line doesn't have an in-body auto focus motor until the D90 camera. The AF line doesn't have an in-lens auto focus motor.

50mm can be used for portraits, although a little bit more focal length would be better. It could be more worthwhile to get the 60mm AF-S macro lens that can do portraits and extreme closeups. 50mm could be good for self portraits that you will probably want to crop, but you would want to have autofocus for that, which the 50mm f1.8 lacks with the D3100.
The AF-S 35mm f1.8 is kind of wide for head and should portraits. It is a nice general use lens which is sharper than the kit lenses.

For portraits, definitely at least 50mm. 35mm is too wide, if you get close enough to avoid excessive cropping, then the perspective will be unfavorable. Big nose, small ears.

As it has been mentioned, there are basiclly three choices now:

The 50mm/1.4G (not D!) will autofocus and is generally an excellent lens. It's much more expensive than any f/1.8 prime though.

The 60mm/2.8G macro lens is good for both portraits and macro shots, but it's also the most expensive of all these lenses.

A new 50mm/1.8G that will autofocus on your camera will be released in a few months. It may be worth it to wait for it.

The 50 but wait a few weeks and you can get one that autofcousses