I am struggling with certain personal aspects of my life, and almost every Christian I ask about this issue seems to be against it. I know there are some few Christian people that are in favour of homosexuality, but they appear to be a minority. This is very important for me, because I understand the Bible does say things about this, but no one I asked (neither those for it nor those against it) has given me the biblical basis for their stance. Some people say I shouldn't worry about what the Bible has to say on the matter, but I am concerned about this, not simply going to church and worshipping but also applying principles to my life. I believe this is the way Christianity should be practised.
1. What you "are" is irrelevant
Let us first distinguish between being a member of a class - in this case homosexuals - and engaging in any sort of behavior. For many people, being a member of the class "homosexual" means having feelings in one direction or another. In no event would a "temptation" towards a certain behavior be taken as exclusion.
James makes it clear that temptation itself is not sin.
Galatians also makes it clear that being a member of any class is irrelevant:
At the risk of self promotion, look at this answer for more.
2. What you do is irrelevant
Even without broaching the question of whether or not homosexual activity is sin, this question still be categorically answered "Of Course you can!"
The primary message of the Gospel is grace. Grace is God's unmerited favor - the free gift that he bestows in which he says "You are forgiven"
Remember that before God ALL MEN ARE SINNERS. As Isaiah 64:2 says, eve "our righteousness is as filthy rags" in God's sight. There is simply no person that God loves more than any other - he is "no respecter of persons"
Furthermore, as Ephesians 2:8-9 states,
3. Whether or not you continue in homosexuality is the only question
Once one is a Christian, one is expected to grow in Christ - to become more Christ-like. Here is where as you mature, you may want to put these things away. But, understand, obedience comes out of love and desire to be more like Christ.
As Jesus says in John 14:12 "If you love me, keep my commandments." It is explicitly not "Do what I say so that I will love you."
Under no circumstances should one believe they need to get clean before being washed by Jesus!
Finally, what you probably want to ask is "Is Homosexuality a Sin" This question has been asked here and here. Gene Robinson, the Episcopalian bishop of New Hampshire who left his wife for another man likes to argue Acts 10 - (Let no man declare unclean what God has declared clean) - that God is doing a new thing. I personally don't think God's word has changed on that matter - but I bring it up to say that Christians debate the matter.
In any case, sin is irrelevant. God's grace is what is important.
Of course you can be whatever you want and be a Christian. The question is whether or not God will leave you that way.
You can be homosexual and a Christian. In fact, Jesus allowed them in his ministry as eunuchs are often considered homosexual.
Matthew 19:12 NIV
However, it has been my experience (my sister in-law is homosexual) that Christians are not as accepting. That is, my sister in-law's partner was a very active member of a Catholic church, a drummer in the band... until they found out she was homosexual. She fears God and believes that Jesus is her savior. I consider her Christian and by the grace of God, I will see her in heaven some day.