Nibbling shrimp cocktails and finger sandwiches, close to100 trade association executives this week heard a soft-shell pitch on why they should move their association headquarters to the Washington area.

Treated to Big Band music andan ongoing slide show in the Mike Mansfield Room in the Capitol Monday night, the executives -- from associations with staffs of 10 or more and budgets of more than $250,000 -- came to town for the 60th annual convention of the American Society of Association Executives (ASAE), which attracted morethan 2,100 association chiefs.

Throughout ASAE's four-day extravaganza, Board of Trade officias planned to be on hand to convince executives whose associations are located elsewhere that D.C. is the heart of the action and the town for a home office.

Kicking off the Monday reception was the expected announcement by the American Society for Training and Development, now based in Madison, Wis., that it will moveits headquarters to D.C. next year.

The 36-year-old organization for human resource development professionals will move its 50-person staff to an undisclosed downtown site.

Monday's $3,500 reception, just one of a series of programs in the Greater Washington Board of Trade's "Case for Washington" program, attracted officials from many area Chambers ofCommerce and business development organizations who hope toincite more executives to pack their bags and join the 2,500 trade associations now based in Washington.

"We're going after any group we can, trying to convince them to move toD.C.," said Robert Tardio, chairman of the Board of Trade'sbusiness development bureau. "If doctors were in town, we'd be going after them. Tonight it's the association executives."

Leaving their traditional homes throughout the country, more than 900 associations have immigrated to D.C. in the last decade. The associations based here -- about a thirdof all national associations -- account for around 87,000 employes and dole out an aggregate payroll of $2 billion yearly, making associations the city's third-largest business.

Many have left Chicago or New York, long heralded as the meccas for association headquarters.

Among the motives cited for moving here are closeness to government and access toother trade associations who share similar lobbying interests.

Though no executives at the Monday night reception --other than those from the ASTD -- would say they plan to move their headquarters here, several said they will expand already established Washington offices. Such an action frequently signals an association's intent to move to D.C. eventually, according to Bob Gray, the board's chief of staff.

Among those planning to expand here is the National Frozen Food Association Inc. Based in Hershey, Pa., that group has had a Washington office since the summer of 1979.

"Washington has become a very important part of our activities," said Richard Funk of that association. "We certainly expect to expand here before long."

So does the Chicago-based National Parent Teachers Association (NPTA), representing 6 million parents, teachers and students, NPTA's story defies the recent pattern: In the mid-1950s, NPTA moved out of Washington to the Midwest. But in 1977, the association moved its govenment relations branch back to D.C.

Having played a major role in the Capitol Hill fights for a tuition tax creditand the newly established Department of Education, NPTA plans to pour more money and manpower into its D.C. office, according to NPTA Executive Director Becky Schergens.

Among the board's most successful strategies luring associations here has been the use of newly arrived executives to detail their experiences locating in Washington.

Not only does a move frequently fragment an association's staff, but it requires formation of new business contacts and location of office space. Executives considering a move like to know how others have done it.

"I came here kicking and screaming," Dick Bozen, senior vice president of the Edison Electric Institute told Monday night's audience "Now I'm sold. tThis is the place to be."

Board of Trade officials plan extensive follow-ups to Monday's event. When they return home, the executives will receive more brochures detailing the "Case for Washington," the board's four-year-old program which it claims has brought 21 associations -- representing 210,000 individuals and 1,600 companies -- to D.C.

The board's Gray predicts that, by the end of 1980, 25 more associations will have announced plans to move here.

"But out work's really cut out for us," Gray said. "We only have 28 percent of allassociations here now. In other words, that's 72 percent we don't have, quite a sizable chunk to lure."