Can an LED starve an MCU of current?
Assuming that your circuit is something like:







simulate this circuit &ndash; Schematic created using CircuitLab

This is the normal way of connecting things, and the LED will not "starve" the microcontroller of power.

The microcontrooler will always see 3 volts from the batteries.  When the micro sets the ouput high to turn on the LED, The micro will deliver current from its output pin which will flow through the LED and resistor.  There will be about 2 volts across the LED, and about 1 volt across the 220 ohm resistor.