enum Stat { ON, OFF };
long pt = 0;
Stat state = ON;

void setup() {
  pinMode(2, OUTPUT);
  pinMode(12, OUTPUT);
  digitalWrite(2, HIGH); 
  digitalWrite(12, LOW);   
}

void loop() {
  long ct = millis();

  switch(state) {
    case ON:
      if(ct - pt >= 3000) { 
        state = OFF;
        pt = ct;
        digitalWrite(2, LOW);    
        digitalWrite(12, HIGH);  
      }
      break;

    case OFF:
      if(ct - pt >= 2000) { 
        state = ON;
        pt = ct;
        digitalWrite(2, HIGH);   
        digitalWrite(12, LOW);   
      }
      break;
  }
}