The Asian Development Bank, buoyed by continued strong economic conditions in its member countries, lent $2.2 billion in 1984, an 18 percent increase over the $1.9 billion it lent in 1983, the Philippine-based bank said in its annual report released last week.

The ADB, an association of 45 nations established in 1966 to promote economic and social development in the Asia-Pacific region, said the gross domestic product of its member countries grew by 5.5 percent last year, a "marginal" decline from 6.3 percent in the previous year.

During 1984, the ADB reported an increase in the average size of its loans, which had the effect of channeling more funds into fewer projects. Last year, the bank approved 49 loans for 47 projects in 18 countries, compared with 55 loans for 53 projects in 17 countries in 1983.

The ADB attributed the lending increase to several factors besides improvement in the region's economy, including the liberalization of bank lending and financing policies and a number of large development projects.

The bank reported a very sharp rise in the number of loans in the energy, transport and communications areas. Loans for energy projects equaled loans for agriculture projects, which together accounted for about 68 percent of all lending. Behind them, transportation and communications projects received $381 million in loans, up from $65 million the previous year.

The annual report says most member countries, with the exception of The Philippines, North Korea, India and Pakistan, posted an increase in gross domestic product last year. The growth rates ranged from a gain of 10.6 percent in China to a dip of 4 percent in The Philippines.

In other important developments in the past year, the bank reported that the dollar amount of cofinancing agreements tripled to $1.2 million from $309 million; the bank's lending rate on ordinary loans declined from 10.5 percent to 10.25 percent; and a South Pacific regional office opened in Port Vila, Vanuatu.