Top officials of Japan's giant telecommunications monopoly, Nippon Telegraph and Telephone Co., tried yesterday to persuade skeptical American business executives that they have a fair shot at selling their products in its $3.3-billion-a-year market, which was closed to outsiders until 2 1/2 years ago.

But although NTT officials, including President Hisashi Shinto, insisted that they welcome imports, Americans complained that the word is slow in filtering from the top through the monopoly's bureaucratic ladder, and they suggested the possibility of an "affirmative action" program of assured contracts to repay U.S. firms for all the years they have been shut out of the lucrative market.

"We hear all the nice things, but it still isn't happening. I think there is a strong bias toward Japanese products further down the line in NTT," commented Richard Dulude of Corning Glass Works after procurement director Ichio Kata described how NTT is making it easier for American firms to bid for contracts.

John Sodolski, a vice president of the Electronic Industries Association, added that the 1981 agreement opening up NTT to U.S. goods is "cumbersome and complex and until today has yielded no positive results."

"Buying decisions in Japan are based on something other than technical performance," Sodolski asserted.

Although the public has largely ignored the low level of American sales to NTT since the signing of the agreemeent--which ends in December--both President Reagan and Prime Minister Yasuhiro Nakasone have publicly expressed concern. Nakasone, conscious of Japan's growing worldwide reputation as being reluctant to buy foreign manufactured goods, reportedly instructed Shinto to increase NTT's foreign purchases.

American sales to NTT totaled $16 million in 1981, the first year of the agreement, and increased to $48 million last year. Shinto has predicted that sales could jump to $150 million by the end of the third year. But Japanese sales of telecommunications equipment to the United States leapt from $400 million in 1980 to $752 million last year amid growing fears that the gap will increase as more Americans buy their own phones.

"The result in concrete sales to NTT has been modest" in the first 2 1/2 years of the agreement, acknowledged Deputy Assistant Commerce Secretary Clyde Prestowitz. And Rep. Timothy Wirth (D-Colo.), chairman of the House telecommunications subcommittee, which together with the Commerce Department has sponsored workshops in five American cities on NTT purchasing policies, said most of those sales have been of the least complex products.

Wirth said that American telecommunications companies, which are considered the most advanced technologically in the world, need to be allowed into NTT's advanced planning sessions so they can design the complex switching and transmission equipment to fit the special needs of the Japanese market.

Many American firms appear wary of making the needed investment to sell in the Japanese market. Attendance in the five workshops has disappointed Wirth and L. Daniel O'Neill, whose Technology Analysis Group has coordinated the events.

"We sent out more than 5,000 invitations, and about 100 have responded," said Wirth. Washington--with NTT President Shinto as the draw--had the best attendence, but O'Neill said only 10 companies showed up in Dallas, and there were 25 no-shows in San Francisco and 10 in Denver.