1993 Toyota Corolla black smoke and smell smoky

Hello, at first I'm sorry if I wrote a incorrect sentence.
Fortunately my car is a healthy & good car & I like it but recently I got that it mostly makes a gray smoke with smell(smoke & smell like a candle is puffing & goes off). Also it decrease engine oil about less than 1liter per 1000Km.
The accelerate and taking off the car is not bad and poor which make me to open the engine for repair or replace necessary parts.
1- I want to know is this oil reduction important I must maintain that as soon as possible or not?
2- Is this oil reduction completely dependent to that smoke & smell which mostly(not always, it appears mostly at the starting engine time and turning off time) is seen from car exhaust?
I'm sorry for my bad & long sentences & questions.
I hope you get my meaning & I hope not to waste your time.
Thank you so much.
Hatam Ebrahimi

updated 2-7-09
Hello,
Thank you for your attendance to my problem. Yes there is a little leakage seen in the engine but it seems to be maximum 5% of oil decreasing. Also again I payed attention on my data about oil deficiency refilling, it seems it's about 500cc in 1000km decreasing which about 5% is for the leakage. Some body says it may be for deforming washers which seal air valves shaft in their holes, (I really didn't know their name, & I hope I was successful to explain what it is!). Is this theory possible or it won't be certain until engine is opened?
Again I'm sorry of my inexact question and thank you for your patience.
Thank you