Automatic gain control in LNA

It is unlikely that a LNA would have AGC. This is because you need a volt or so of RF to be detected to then channge the gain determining network in the LNA. If a LNA is dealing with signals in the order of micro or millivolts then there is not enough RF to be rectified. You could have a side chain which has additional gain to get enough RF to do something with. The normal thing is to use the output of the IF amplifier to be used as the source of the AGC voltage.
If you just want to change the gain of the LNA in response to a large input signal, then changing the DC bias will normally work over a small range, say reducing the gain by 15 dB or so. Forward biasing the transistor results in very low input impedance that damps the tuned circuits and is less likely to produce IPs. Sort of normal Ic= 2mA when running at minimum gain Ic = 50 mA.
Frank

If AGC circuit can rectify so that RF signal has sufficiently large signal level, LNA can be controlled by a negative feedback circuit.

thanks for the reply,but what is the need for automatic gain control in LNA or when do we need it?

You need to make sure that the gain of the LNA can be reduced if the input signal is too great. if there is no gain reduction, then it or subsequent stages may be over loaded and produce IPs, which will results in spurious responses.
Frank