LOS ANGELES — The rise in tuition at public colleges slowed this year to the smallest increase in more than three decades, although financial aid has not kept pace to cover the hikes, according to a College Board study released Wednesday.

At public four-year colleges and universities across the country, the average price for tuition and fees rose 2.9 percent this year — the smallest annual rise in 38 years — to $8,893 for in-state students, the report said. Room and board adds about $9,500.

However, analysts urged students and families to pay closer attention to what they described as the more important figure: the net average cost after grants, tax credits and deductions. That was $3,120, up from $3,050 last year, for average net tuition and fees at four-year public colleges.

“It does seem that the spiral is moderating — not turning around, not ending, but moderating,” said Sandy Baum, a co-author of the College Board study and research professor at George Washington University.

Baum said the relatively small increase, while still above the general 2 percent inflation, was good news and she hoped it will encourage more students to enroll in college and apply for financial aid.

The tuition hikes at four-year public colleges from 2010 through 2012 had averaged 7.9 percent, 8.5 percent and 4.5 percent, respectively.