In a city where designer ties and natty tailoring are the rule, there was no mistaking where the boxy suits and plastic briefcases hailed from. China had sent the largest ever delegation of mainland mayors, trade officials, engineers, interpreters and secretaries to Hong Kong to promote the 14 coastal cities opened up last spring to foreign and trade investment.

These cities join China's four special economic zones as places where foreign investment earns special low tax rates and other incentives to aid China's modernization.

More than 500 Chinese delegates, only 150 of them "official," descended on Hong Kong recently, many of them getting their first glimpse of the British colony where more than 5 1/2 million Chinese residents mix freely with foreigners and enjoy a capitalist life style that to mainland eyes seems luxurious beyond belief.

The enthusiasm of the delegates and their eagerness to tap this seemingly limitless source of foreign financing was obvious. Clearly, tailors from Lianyungang to Beihai had been busy for months running up western-style suits for first-time travelers bidding for the attention of more than a thousand foreign businessmen at the 10-day investment symposium that began Nov. 5.

The delegates' excitement was heightened by the Communist Party endorsement only a few weeks before in Beijing of Deng Xiaoping's economic reforms. Policies such as cost-accounting, price reform, worker incentives and taxation instead of state subsidies were extended to urban as well as rural areas. More than ever before, China's cities, and particularly the coastal cities assigned to lead development, are in a race for overseas technology and capital. Scattered in hotel rooms and offices throughout Hong Kong, visiting Chinese officials hustled hard to obtain at least a letter of intent from foreign companies before their 10 days were up.

"It's starting to look like the Canton trade fair of investment projects," said an American businessman with years of China experience.

Although the 14 coastal cities all offer similar investment incentives, they are hardly in the same league in terms of size, services and relative economic development.

Some of the cities were more complacent than others about the importance of the symposium to their development plans. Shanghai, China's largest industrial center; Dalian, China's biggest foreign trade port; Guangzhou, Hong Kong's bustling neighbor; and Tianjin, a major industrial city in the northeast, have all established regular contacts with foreign companies and banks.

Despite some naivete on the part of the Chinese, preparation on both sides had visibly improved since the first investment seminar was held in Guangzhou in the spring 1982.

"The Chinese just rattled off a list of 107 projects and expected us to rush forward with the money," said a British banker working for a large American bank." This time even the smaller localities had brought rudimentary studies, promising fuller "feasibility reports" once a letter of intent was signed.

This time some 207 projects were earmarked for promotion, and by the end of the 10-day period, China's deputy minister of foreign economic relations, Wei Yuming, announced that 441 had been signed, although many were not on the list, and others had been negotiated long before the Hong Kong sessions began. Forty-three contracts totaling $250 million, 149 "agreements" worth $2.2 billion, and 249 letters of intent with a value of $2.5 billion yielded a possible grand total of $4.95 billion.

Tianjin appeared to have bettered the others, with around 40 agreements signed. A representative of Tianjin's commission of foreign economic relations and trade, Liu Hongyi, said the projects ranged from equity joint ventures to contracts for spare parts, and covered everything from consultations on Tianjin port development to bicycle contracts to a cosmetic surgery clinic.

Lie commented that, generally speaking, his first visit to Hong Kong had only confirmed his impression that the United States was readier than Japan to pass on its technology.