Assuming that the oil under the car is engine oil - it should be somewhere between honey colored and black (in which case you really need an oil change). If it is more red or pink, then it is most likely PS fluid.
If it's engine oil that's leaking - as evidenced by the low oil level - you have two separate issues as engine oil level won't cause a steering noise. Clean the engine bay, drive it for a day or two and check for leaks at the oil pan and around the engine, once your steering issue is fixed.
Your steering issue is due to one of:
- Dying power steering pump. This isn't all that surprising with 150k on the odometer.
- Low on power steering fluid, which can also lead to (1). It could leak from the reservoir, pump, rack or hoses connecting those.
- Faulty steering rack, though I've never heard a bad rack make that noise.
- Obstructed hose on the steering rack. This is very rare.
Check your PS fluid level, make sure that the belt is tight (though you would probably get a squealing noise if the belt is the issue). If it is not tight, check the belt tensioner.
Replace the pump. These can be had used on ebay for $40, or at your local parts chain store for around $90 US.
If the level is good, you can try flushing the PS fluid, but given the cost of having that done, you may be better off just replacing the pump. If by "power steering is cutting out" you mean that the assist goes away, I'd suspect the pump. I've changed a number of those in my day - it's usually not difficult - but have only had one steering rack go bad on my cars.