Millions of young Americans are filling out federal tax returns for the first time as Friday's filing deadline approaches, and many of them are learning that you don't always get a refund.

Several new provisions affecting students who work part time and youngsters under the age of 14 took effect in 1987 and are being felt on returns filed this year. The net effect is to complicate the finances of these people and, in many cases, of their parents.The Internal Revenue Service estimates 3.3 million people are having to file returns for the first time because a section of the 1986 law denies a personal exemption, worth $1,900 for 1987, to those who can be claimed as a dependent by a parent or someone else.

In addition, young people can lose a good portion of their $2,540 standard deduction by being claimed by a parent. And thresholds for filing are lower than in the past.

Two other new provisions:

Any child 5 or older who is claimed as a dependent must have a Social Security number, which must be listed on the parents' return. The IRS has waived the penalty for not listing the number on 1987 returns, but it's still required.

Any investment income exceeding $1,000 received by a child under 14 is now taxed at the parents' higher rate, assuming that is higher than the child's rate. These calculations must be made on Form 8615, which must be attached to the child's return.

Congress imposed this requirement to block mainly higher-income parents from avoiding taxes by shifting income-producing property to a child. Under the old law, a parent could have avoided $390 of tax on $1,000 worth of interest that was credited to the child's account, paying $110 instead of $500.

This "kiddie tax" provision has been a source of anguish for taxpayers, experts say. "There is more confusion in trying to fill out the forms than there is surprise about so many minors having to file for the first time," says Vern Martens, senior tax attorney at Merrill Lynch headquarters in New York.