Up and down the hotel corridor there were registration tables, yellow T-shirts with the Alpha Phi Alpha fraternity insignia for sale, and greetings of "brother," as Alpha men from Hartford to Williamsburg gathered for a regional meeting.

As one indication of the growing strength of blacks in the suburbs, this meeting did not take place in a typical downtown Washington setting but 12 miles away in New Carrollton.

The Washington area has became a pacesetter for the transition of the traditional organizations - and the accompanying professional and social contacts - to the new suburban lifestyles. The Alpas, for one, are actively testing their political and civic clout in the new arena.

"Washington is a fore runner of what can be expected as more Alpha men spread out geographically," said James R. Williams, the national president, as he watched nearly 300 men and their families register yesterday.

In recent years the half-dozen or so leading black fraternities and sororities have dramatically shifted to an almost exclusive social service emphasis.

In the late 1960s when the fraternal groups were attacked as too partyminded, their memberships dropped. They have reemerged on the campuses, however, principally because of substantial projects such as funding movie productions and housing projects.

The A lphas, the oldest predominatly black fraternity, predating the NAACP and the National Urban League, has an international membership of 75,000. Since its founding in 1906 at Cornell University, members have included Martin Luther King Jr., Whitney Young, Paul Robeson, Thurgood Marshall. Edward Brooke, Adam Clayton Powell Jr., four current congressmen and three mayors.

While the national memberships has grown, initiating 3,500-4,000 new members last year, the suburban chapters have shown similar growth.

The Montgomery County chapter was started in 1970 with 35 members. It now has 142. Two years later 13 Alphas formed a Prince George's County chapter, which now has 35 members. In the last five years, the 14-year-old Arlington chapter has grown slowly from 60 to 71 members but the area also has a large transient military population.

Floyd Wilson, the vice chairman of the Prince George's County council; Anthony Jones, a prominent architect; William T. Syphax, a well-known builder, Thomas Penn, chairman of the Arlington County school board, are members. Roscoe Nix the only black member of the Montgomery County school board, is pledging the fraternity. Williams, the president, was recently appointed U.S. attorney for the Eastern District of Ohio.

"In Arlington, a major thrust is to make sure some of us are involved in the important civic committees," said Clarence Halstead, who recently retired from 31 years in the school system. In northern Virginia, where the average Alpha is 35-40 years old, the chapter has a scholarship and Big Brothers program, as well as a clothing drive.

While all of the chapters have traditional programs, such as scholarships (and the national fraternity has a major $1 million fund-raising drive in progress for the NAACP, the Urban League and the United Negro College Fund), some of the newer chapters are moving in a political direction.

Kenneth E. Clark, 32, an engineering manager for the C&P Telephone Co. and the President of the Montgomery County chapter, said, "As an organization we want to take a stand on issues and then put pressure on county officials."

That chapter, which has been cited by the national as the most active in the country, has sent telegrams to the White House on the Bakke affirmative action case, sponsored forums with county educators on the needs of black children in the schools, and compiled a directory of minority businessmen in the county.

"What you will find," said Robert Hatchell, a school administrator and past president of the chapter, "What we are finding is that the Alphas are respected because we have a vast array of resources."

As its first project, the prince George's Alpha chapter developed a directory of black leaders. "We saw the movement of blacks and wanted to get involved in shaping leaders, but first we wanted to identify and then ally ourselves with the existing leadership," said James Trent, 44, a Department of Interior official.

When the chapter decided to focus on educational issues, it attracted Randolph Williams, an inactive member for several years.

"Many of the Alphas in the county were teachers. I then had two kids in the public schools and busing was going into effect and I wanted a voice," said Williams, a laboratory technician at the National Bureau of Standards.

Like their national president, many of the 500 Alphas attending yesterday's meeting, didn't think the suburban location would change the Alpha fabric. "Basically black people need the same thing wherever we are - advocates and leaders. But I think the suburbs has just made us more cohesive and bolder in that effort," said Trent.