In order to be under cover you have to lie a lot!! How would God look at this?
The answer to your question is determined by the meaning of the word “lie.” It is clear from scripture that God does not approve of lying. In the book of Numbers, our holy God declares that He is not like us because He does not lie. We do not tell the truth.
God is not a man, that He should lie, Nor a son of man, that He should repent; Has He said, and will He not do it? Or has He spoken, and will He not make it good? (NASB) Num. 23:19
As a young father I was extremely surprised the first time that I heard one of my daughters lie. I remember thinking to myself that what she wanted me to believe as the truth was so impossible that I almost laughed. It was just an incredible lie. She had not learned that from my wife or myself. Her sin nature was sufficient.
The Hebrew word for lie is AKZAB and it means “to speak that which is untrue and therefore false to reality . . . In distinction from words translated ‘deceive, lie,’ etc., KAZAB stresses the actual act of lying.”  A person lies when he or she intentionally, willfully and knowingly deceives another individual.
False testimony is a form of lying. One of the Ten Commandments gives us this warning,
You shall not bear false witness against your neighbor. (NASB) Ex. 20:16
Lying is a choice that a person makes to deceive another person about either himself or herself or another individual. Lying is the result of a sinful heart.
Some people have struggled with the following passage of scripture.
Now the LORD said to Samuel, “How long will you grieve over Saul, since I have rejected him from being king over Israel? Fill your horn with oil and go; I will send you to Jesse the Bethlehemite, for I have selected a king for Myself among his sons.” But Samuel said, “How can I go? When Saul hears of it, he will kill me.” And the LORD said, “Take a heifer with you and say, ‘I have come to sacrifice to the LORD.'” (NASB) 1 Samuel 16:1-2
Some believe that God directed Samuel to misrepresent his intended actions. But a careful examination of King Saul’s coronation ceremony reveals that sacrifices were offered when he was made the king of Israel (1 Sam. 11:15). Therefore, we discover that God reminded Samuel that a sacrifice had to be offered at the next king’s coronation. God directed Samuel to tell the truth but not to reveal everything. The book of Proverbs reminds us that we do not always need to say everything, nor should we.
When there are many words, transgression is unavoidable, but he who restrains his lips is wise. (NASB) Prov. 10:19
Do you see a man who is hasty in his words? There is more hope for a fool than for him. (NASB) Prov. 29:20
Lying is claiming that something is true when it is false. Sometimes we provide more information than is necessary. To withhold information is not lying, but to state something that is not true is a lie. Barnes’ Notes makes this comment about the passage,
. . . secrecy and concealment are not the same as duplicity and falsehood. Concealment of a good purpose, for a good purpose, is clearly justifiable. 
John Murray (1898-1975), professor of Systematic Theology at Westminster Theological Seminary in Philadelphia, Pennsylvania makes this comment,
This incident makes clear that it is proper under certain circumstances to conceal or withhold part of the truth. Saul had no right to know the whole purpose of Samuel’s mission to Jesse nor was Samuel under obligation to disclose it. Concealment is not lying . . . This passage is perhaps unique in the Scripture because there is the explicit authorization of the Lord as to the method of concealment. It is just for that reason that the precise conditions are to be observed; there is no untruth involved. It is necessary to guard jealously the distinction between partial truth and untruth. If we are not hospitable to this distinction it may well be that we are not sensitive to the ethic of Scripture and the demands of truth. 
How does this apply to your question? There is nothing wrong with concealing information, but it is wrong to purposefully state an untruth. Scripture teaches that there is nothing wrong with going to war and killing the enemy. Yet, we are commanded not to murder. The difference is 1) God established the principle when He directed Israel to go to war and 2) the solders were not acting alone.
From this short study we discover that it is not wrong for an under cover agent to conceal information. It is more problematic if you must claim that you are something that you are not. There are no clear biblical examples or patterns available to answer your question; however, Ezekiel 33:6 implies that a policeman is obligated to protect the citizens. Law enforcement officers do not act on their own usually. They are motivated typically to protect the citizens. That is, they do not lie intentionally for some personal overt benefit such as wealth, reputation or glory. The same is true of soldiers. Is there a parallel principle to a soldier’s defense of a country? If soldiers can take a life without being accused of murder can law enforcement lie to protect the citizens?
1. Harris, Archer, and Waltke. Theological Wordbook of the Old Testament. Moody Bible Institute. vol. 1. p.435.
2. F. C. Cook, editor. 1 Samuel., The Bible Commentary. Barnes Notes. Baker Books. 1996. p. 40.
3. John Murray. Principles of Conduct. Eerdmans Publishing. 1957. p. 140.