The first day of national draft registration came quietly to the Washington area yesterday -- a passionless trickle of 20-year-olds marching to post offices amid a scattering of small low-key demonstrations staged by local antiregistration groups.

Selective Service System officials said it was too early to tell how many of the approximately 5,000 area youths born in January, Feburary and March 1960 actually registered yesterday as required at the 200 post offices.

Jimmie Harrison, a 20-year-old who had just crossed a picket line at the Main Post Office in Washington, seemed to sum up the feelings of many of the young men interviewed yesterday: "I'd rather go to them and sign up than have them come looking for me out in the streets."

Attitudes aside, Selective Service officials said registration -- the first in the United States since April 1975 -- appeared to be going well yesterday.

"The word from post offices around the country is that things are going fine . . . quietly and smoothly," said Joan Lamb. "We won't know what kind of turnout we had for at least 90 days, when we get the data compiled."

Brayton Harris, assistant director of Selective Service, said he expects about 98 percent compliance over the two-week registration period.

The new registration, enacted by Congress last spring in response to the Soviet invasion of Afghanistan, will continue through Aug. 2, with all males born in 1960 registering this week and those born in 1961 next week.

Men born in the first months of the year were to register yesterday or do so next Monday, depending on their year of birth. Men with April, May or June birthdays should register either today or next Tuesday. Those with July, August or September birthdays should register tomorrow or next Wednesday, and those born in October, November or December should sign up either this Thursday or next Thursday.

Fridays and Saturday mornings are makeup times for those who cannot register on their designated dates.

The Rev. Barry W. Lynn of the National Committee Against Registration and the Draft, predicted that a full 15 percent of all eligible young men would not register, citing "resistance, anger" and confusion over last week's court decisions, in which a three-judge federal court in Philadelphia first declared registration unconstitutional, only to have a stay issued by Supreme Court Judge William Brennan, giving the U.S. government a chance to appeal the ruling before the full Supreme Court this fall.

Small groups from various antiregistration coalitions set up tables yesterday outside several post offices offering counseling, information packets and "I am registering under protest" stickers to attach to registration forms. a

Singing Vietnam-era antiwar songs like "down by the Riverside" and carrying placards declaring "Hell no, we won't go, we won't fight for Texaco," about 30 demonstrators took their places in the sweltering heat outside the District's main post office to "help out some of these kids who are kind of confused about registration," said Jan Midgely, of the Washington Area Coalition Against Registration and the Draft.

Inside the post office, however, several youths filling out registration cards said they were in no way confused and that registration was a legal reality they had to deal with.

"Some people feel that the draft is not worth it," said Kennedy McCrory, a dishwasher at the National Art Gallery. "But the law says we have to register. It ain't no use fighting the government -- we'd just be fighting ourselves . . . Let those people outside protest and have their fun -- it ain't gonna do nothing anyhow."

Outside the Selective Service System national headquarters at 600 E Street NW, a group of about 20 demonstrators tried to make their statement through civil disobedience, sitting down in front of the building entrance in hopes of blocking incoming workers.

A dozen burly Federal Protective Service officers and about 30 D.C. police pushed, pulled and carried determined and emotional demonstrators from the doorway so building employes could pass, only to have the protestors pop back into place.

After three hours of shoving and an appearance by Assistant Selective Service director Harris, the demonstrators left.

Elsewhere throughout the metropolitan area, young men came alone or with friends to register -- to do what they said they had to do, like it or not.

"I don't really want to go to war, but I figure if you got to do it, you got to do it," said Donnie Simpson, a graduate of T.C. Williams High School, as he filled out his card at the Old Town Alexandria Post Office on Washington Street. "Besides, I just read here that if you don't register, you get fined $10,000," he said.

Young men who signed in at Montgomery County post offices had many of the same comments. Most interviewed said they did not see any serious consequences resulting from registration. Many said they saw it as a responsibility. "This is the first thing in my life that's ever been mandatory, so it's a big deal," said one.

It went about the same way across the country.

In Hartford Conn., eight protestors were arrested when they entered the main post office there and disrupted operations. But when four women chained themselves to a post office desk in Kansas City Mo., registrants simply stepped over them.

And is Sioux Falls, S.D., things went a little differently. Turning away one man who wanted to volunteer, a clerk smiled and told a reporter," He was born in 1917."