If the opening rounds of President Carter's draft registration program were quite in your town, you should have been in Boston.

Following a weekend of legal maneuvering and massive confusion nationwide, registration of 19- and 20-year-old men began on a steamy hot Monday morning in Post Office square.

More than the streets were hot at day's end, however, as anti-draft demonstrators' attempts to blockade the city's main post office brought first the police--then a nearby crew of construction workers, offering physical help and singing "God Bless America."

Police had arrested more than 30 demonstrators--the first in a series of local confrontations that included a failed attempt to chain closed the doors of the Central Square post office and a successful shutdown at the Harvard Square post office.

National opponents predicted that draft registration will go down in history along with Whip inflation Now buttons and swine flu innoculations, while Selective Service officials have contended that 98 per cent of the 4 million young men asked to sign up will comply. But meanwhile, figures showed that as many as 25 per cent in the area may not have listened to Cater's call to arms.

About 32,600 local males registered for the draft--a figure compiled only because one postal service employee believed the numbers would be useful in case it happened again.

As the two-week sign up period wore on, leafletters remained stationed at post offices, but the highly charged atmosphere of the first few days gradually dissipated.

Local experts in constitutional law, however, predicted that the fireworks would be launched again this fall, when the Supreme Court considers a lower court's ruling that draft registration is unconstitutional because it discriminates on the basis of sex.

That decision--issued by a Philadelphia district court in a nine-year suit by three men who were drafted during the Vietnam war--overshadowed a similar case filed in Boston just before the sign up period began.

At the Law School, several professors close to the high court, said that, given the Supreme Court's record in sex discrimination cases, it would overturn the Philadelphia decision and proclaim the program constitutional, Others disagreed, however, saying the lower court would be upheld.

Even liberal justice William A. Brennan claimed that the high court's chances for overturning the case were only "fair."