Author Alex Haley, in Washington on a whirlwind one-day visit, triggered an enthusiastic response yesterday when he said that he believed his book, "Roots," had helped to dispel a myriad of myths about the capacity of blacks to contribute to the American society.

"Traditionally, we have dealth with the self-perpetuating myths that blacks were 'less than . . . or less able than' someone else," Haley told the group, composed largely of minority businessmen and representatives of major corporations.

Haley, the author of the bestselling book, whose themes were recreated in a nationally popular television series, was the keynote speaker at the 1977 Opportunity Fair of the Greater Washington Business Center.

"Across generations the potentials of a whole people has been stunted and poured down the drain," Haley asserted. "This meeting shows that we're now doing something to correct the injustices."

The Greater Washington Business Center was created in 1975 to help promote minority businesses in the Washington metropolitan area and the nation. The Opportunity Fair, held annually, is an effort to bring minority businessmen together with majority corporations to provide a mean of developing contacts.

At yesterday's luncheon at the Washington Hilton Hotel, where the fair is being held, the organization presented the first annual economic "Roots" award to soul-rock recording executive Al Bell, former president of Stax Records, of Memphis. Bell recently relocated his firm in Washington under the name, Independence Corporation of America.

The minority businessman of the year award was presented to Don King, president of Don King Productions, Inc., the firm that promotes the fights of heavyweight champion Muhammad Ali, King's firm reportedly grossed more than $100 million last year.

Rep. Cardis Collins (D-III.), who introduced Haley, called him "a really great American - a man who has given us great pride in our past." She noted that as of Feb. 18, "Roots" had sold 999,454 copies, with another 250,000 copies back-ordered and yet to be printed.

"Through the book 'Roots' Mr. Haley has provided us with an invaluable reaffirmation of our black heritage," said Rep. Collins.

Haley, who had been busy signing autographs during the award presentations and his own introduction, received a standing ovation as he approached the podium.

"It still startles me when I hear someone say that I've done all of this," Haley told the audience. "I do not believe it is something I have done by myself. I believe that I have only been a channel - a conduit that has been used at this particular time to tell the story of a people."

In the book, Haley traced the maternal side of his family from his native Henning, Tenn. back to the west coast of Africa. His 45-minute speech yesterday focused on the paternal side of his family.

Haley said that his father grew up in the small town of Savannah, Tenn. where he completed the local school for blacks, where schooling ended at the eighth grade. With $50 and everything, he owned in a small bag, he went on to a nearby "college," which began with the ninth grade and included the second year of college.

Haley said his father worked at four jobs to go to school and because he devoted so little time to actual study, earned only a D grade average during the first years.

But, Haley said, his father eventually was able to go to college for a full year with his tuition paid by a white man who met the young student one summer while he was working as a Pullman porter.

His father eventually graduated from A & T College in Greensboro, N.C., and received a master's degree in Agriculture from Cornell University, Haley said.

Without his father's accomplishments, Haley said that he, and his brothers, George, a lawyer, and Julius, an architect, may have grown up in a family of tenant farmers rather than in a home with educated parents, and the impetus for "Roots" might have been lost.

Haley urged the audience to regard the older persons in their communities as a "precious resource." He said these older citizens should be sought out and interviewed.

"These people can pass on to us information about the preceding generations that we have not before known," Haley said.

Haley also suggested that families save their old trunks of memorabilia and hold annual family reunions at which a family's genealogy could be discussed.

After his speech, Haley was besieged by persons seeking his autograph. Small beads of perspiration rolled from his forehead as he labored to sign - one by one - the hundreds of books and programs that were thrust before him.

Haley was scheduled to present another lecture last night at the Smithsonian Institution's National Museum of History and Technology. Later in the evening, he was to speak at the Foxtrappe social club in a program to benefit Africare, an organization that raises funds to help the needy in African countries.