To all:
sorry for confusing all. I used the external interrupt only once.
once it interrupts and starts the pulse generation routine, the exernal
interrupt is masked, not used again. remaining thinks done in pulse generation
routine.

To EriK:
i have tested the code as suggested by you. for this i cleared the P1.4 pin initially,
once the external interrupt occurs, the P1.4 is SET.
after executing the program, i connected the GND pin to the P3.3(INT1) pin,at that
moment the interrupt occurs.(H to L occurs)
so the problem with the function generator is, it starts from zero only, so while
connecting the function generator to the pin itself makes the interrupt(as it is low)
i am working with circuit which give High intially and goes Low after sometime, so it
could give the interrupt. later i post the result.

To Mehdi:
thanks for your suggestion to use interrupt flag instead R1 flag.
i have given answers above for your 2 questions