I am married and now in USA (H1B). But I have my family in my home country and have one kid. Still I need to submit the W4 form as Single? Whether there is any way to claim the Tax refund for the expense for the dependents.

Also I have the House loan in India. Is that can be shown to reduce the taxable income?

QUOTE," But I have my family in my home country and have one kid. Still i need to submit the W4 form as Single? "--I don't know how long you've been in the US.
Assume that you have been in the USfor the entire tax year (I mean you came to the U.S. as an H-1B visa holderbefore January 1, 2010), then you are considered as a resident alien andcan file IRS Form 1040, 1040A or 1040EZ( if youdo not claim itemized ded.).Also you should pay both state(if applicable) and fed. Taxes and are liable to pay FICA taxes. You also can claim all the exemptions and credits which are available to U.S. citizens, to include filing jointly with your spouse (even if she is living in India) and also claiming the exemptions for your children.
Even if 2010 is your first year( regadless of entering either before July 2nd or after July 1st), as being a married person, you and your spouse can both choose to be treated as resident aliens.
"hether there is any way to claim the Tax refund for the expense for the dependents"----you can claim your spouse and children as dependents as said above as resident alien.
"Also i have the House loan in India. Is that can be shown to reduce the taxable income? "---When filing your joint tax, you can get tax credit on your house mortgage internestpayements that you 'd paid in India.

1. When did you enter the U.S. on H1-B?
2. A dependent must be citizen or resident of the U.S. If you are resident of U.S. that is you meet substantial presence test, you can claim your kid if the kid is in U.S. for any part of the year. Your U.S. Tax Return: Substantial Presence Test (http://taxipay.blogspot.com/2008/04/substantial-presence-test.html)
3. Spouse is never a dependent. You can file joint return if you are eligible to file resident return.
4. Home loan interest deduction is itemized deduction. You can take the deduction provided you withhold U.S. tax on interest payment to the foreign lender.