FARMINGDALE - Applying for student loans could get a lot more stressful for college entrants across the country if Congress doesn't make its tentative loan deal stick before Sunday.The interest rate on federal student loans will nearly double, from 3.4 to 6.8 percent, if Congress doesn't stop the hike before the weekend.Lawmakers in Washington say they've reached a tentative last-minute agreement to halt the hike for another year. If approved, the $6 billion deal would be paid for by cutting some corporate tax breaks and by limiting federal subsidies of student loans. The deal would affect new loans starting July 1, impacting an estimated 7.4 million students. On a $5,500 loan for a semester, the difference would be about $1,000 in interest.