Boston ? If you’re looking for the science that matters most in Washington these days, it’s political science. The answer to everything from global warming to mercury in the water seems to be found in the dubious data of ideology.

Nevertheless, for one brief moment it looked like the Food and Drug Administration actually was going to weigh the evidence on an objective scale. In December, an advisory panel voted 24-3 to recommend that emergency contraception be sold over the counter and without a prescription. It looked like a done deal.

The morning-after pill, or Plan B as it is memorably named, occupies a rare patch of common ground in the struggles over abortion. If there’s one thing that both pro-choice and pro-life people agree on, it’s the desire to reduce the number of abortions.

Of course, Atty. Gen. John Ashcroft wants to reduce abortions by pillaging the medical privacy of doctors and scaring patients. And President Bush wants to reduce them by sneaking anti-abortion Judge William Pryor on to the bench while the Senate is on vacation. But most of us want fewer unintended pregnancies.

Plan B, as the name implies, is the backup when Plan A fails. It’s the second chance to avoid pregnancy … after sex. It’s what you can do instead of waiting in a high state of anxiety.

The technology has been around since the birth control pill. It’s more or less what women do when they forget to take the pill one day; they take more of them the next day. Taken soon enough, you can prevent over 75 percent of the pregnancies.

Emergency contraception is already available with a prescription from a doctor. The problem is the word “emergency.” Ever try to get a medical appointment the Sunday morning after the night before?

That’s not the only hassle. In Texas last month, a rape victim handed her prescription to a pharmacist who took it in the back room, prayed, called his pastor and then refused to fill it on “moral grounds.”

Just for the record, Plan B is not an abortion pill. The Texas pharmacist, like many political scientists, seems to have skipped the core course on “Bio for Babes.” Contrary to the notion that sperm travels at the speed of light, it takes up to 24 hours for an egg to be fertilized and some three days to make the uncertain trip into the uterus. The after-the-act contraceptive prevents pregnancy; it doesn’t work if you are pregnant.

But after the FDA advisory committee agreed that it was safe to sell Plan B over the counter, there was a flurry of letters from conservative members of Congress. “The new fight,”‘ says a frustrated Kirsten Moore, president of the Reproductive Health Technologies Project, “is that it will lead to teenage promiscuity.” The FDA has chosen to “review” this question for as long as another trimester. Do I hear the beakers of science crashing again on the administration’s floor?

We’ve just had another batch of good news on the teen front. The rates of pregnancy and abortion continue to go down, a full 28 percent in the last dozen years. It’s widely agreed by researchers that this is due to both less sex and more birth control. Plans A for abstinence and B for better contraception.

But many on the right continue to argue that the message of abstinence is undermined by the message of birth control. Their Plan A is Abstinence or Else. Indeed the Virginia Legislature is considering a bill to take emergency contraception out of health clinics at public universities.

Why has it been so hard to make emergency contraception easy? There is no evidence that having the morning-after pill available on the drugstore shelf leads teenagers or any other women down the path of unprotected sex. There is, on the other hand, a whole lot of evidence that a backup will prevent pregnancy.

“If the FDA were to go against its advisers, it would deny the evidence,” says Moore, “and take away the possibility of getting some common ground on this issue and giving women a second chance to reduce the rates of unwanted pregnancy.”

Most of us who have had or been teenagers know that vows of abstinence break at least as easily as condoms. I remember a state legislator who used to say, cheerily, “that if you are going to play, you have to pay.” He seemed buoyed by the idea that sex was punished by pregnancy.

But our country still has 3 million unintended pregnancies per year, the highest rate in the industrialized world among adults and teens. Half of them end up as abortions. This is where pro-life ought to meet pro-choice. And this is where we should get the politics out of the science and get Plan B on the drugstore shelf.

Ellen Goodman is a columnist for Washington Post Writers Group.