THE Communist Youth League will hold its 13th National Congress on Monday to pick the eventual successors to the leadership. The meeting of the league, the traditional training ground for the national leadership, has attracted widespread attention because its current leaders have, in recent months, been transferred to key party and government posts. Chinese sources said it was likely that the new party committee of the league, which will be endorsed on May 10, would be ''reliable'' cadres who were reformist in economics and conservative in politics. The sources said the league, which has 56 million members, had regained its status as a centre for grooming new leaders after a period of disgrace soon after the June 4, 1989 crackdown. For about a year after the Tiananmen Square crisis, leading cadres of the league were criticised for the large number of members who took part in pro-democracy demonstrations. According to a report in yesterday's China Youth Daily, the major goal of the 13th congress was to ''encourage league members and youth to throw themselves even more enthusiastically into reform, the open door policy and modernisation''. The China Youth Daily, which is the mouthpiece of the league, added that ''the guiding light of the organisation'' would be patriarch Mr Deng Xiaoping's theory on building socialism with Chinese characteristics. The paper said 1,420 delegates to the congress, who would cast votes for the new party committee, had already been chosen from party, government and military units all over the country. Almost 74 per cent of the delegates are league cadres in various party and government units, while about 26 per cent are ''advanced model figures'' from sectors including industry, agriculture, commerce and the military. Their average age is 30, and more than 76 per cent have a college education or higher. Sources close to the league said most of the members of the party committee had already been promoted to senior party and government positions. For example, at the recent National People's Congress, League First Party Secretary, Mr Song Defu, was made a Minister of Personnel. Earlier this week, Party Secretary Mr Zhang Baoshun, was named a vice-director of the New China News Agency. Mr Ji Bingxuan, a party secretary in the city of Xinxiang in Henan Province, was recently promoted to the league party committee. ''Former leaders of the league, including the late party general secretary Mr Hu Yaobang and the Minister of Electronics, Mr Hu Qili, have been noted for their radical reformist views,'' a source said. ''It is unlikely, however, that the party leadership would pick candidates with liberal tendencies to head the league.'' Former associates of the two Hus still occupy senior positions in various provincial administrations.