PORTLAND – Abortion rights supporters and opponents find different explanations for why Maine has the lowest abortion rate in New England.

Maine’s abortion rate skyrocketed after the U.S. Supreme Court legalized the procedure 30 years ago this week, according to a new report by the Alan Guttmacher Institute.

The number of abortions in Maine jumped from 710 in 1973 to 5,690 in 1981, according to the institute’s survey. The rate slipped until the mid-1990s and then leveled off.

With 9.9 abortions per 1,000 women, or 2,650 abortions, Maine had the region’s lowest rate in 2000. Nationally, the rate was 21.3 abortions per 1,000 women.

New Hampshire had New England’s second-lowest rate with 11.2 abortions per 1,000 women ages 15 to 44. Vermont had 12.7, Connecticut had 21.1, Massachusetts had 21.4 and Rhode Island had 24.1.

Researchers say one reason for Maine’s low rates may be falling teenage pregnancy rates, partly because of an increased use of contraception since the rise of AIDS.

“It could be due to emergency contraception, as well,” said Rebecca Wind, a spokeswoman for the Guttmacher Institute, which supports abortion rights but whose data are used by activists on both sides of the issue.

The institute found that so-called “morning-after” pills may have prevented more than 50,000 abortions in 2000.

While the opposing sides of the abortion debate are both pleased with the decline, supporters link the trend to increased awareness of contraception and opponents attribute it to changing social mores.

“After living in the shadow of Roe v. Wade for 30 years, young people have seen the pain caused by abortion and are consequently going in an opposite direction,” said Marc Mutty, spokesman for the Roman Catholic Diocese of Portland.

Dr. Dora Anne Mills, the director of the state bureau of health and a vocal supporter of abortion rights, said sex education and increased access to contraception has reduced both abortion rates and teen pregnancy rates.