Water pressure had been diminishing on a Moen lever kitchen fawcett. Now there isno pressue at all

Remove and clean your aerator. Aerator is the screen / filter on tip of your kitchen faucet. Usually, it is hand tighten.

Milos advice about checking the aerator,(see image) is the first thing I would check. However,if that doesn't get it perhaps you have some crud of the pipe walls blocking the inlet ports on the cartridge. Here'sa typical Moen kitchen faucet,( see image). Shut the water off and remove the cartridge,( if you need instructions just click on back.) Check and clean the cartridge inlet ports. Now turn the water back on to flush out the supplies aqnd open valve body. You should have a strong stream when you do this. If not, then let me know. If you have a strong stream then reassemble and test. Good luck, Tom