RIVALRY between Beijing and the regional governments is expected to increase given the central Government's determination to significantly increase its share of national revenue. The latest issue of the weekly Outlook reveals that the major thrust of the reforms, which will be announced at the forthcoming third party plenum, is to boost the national treasury's share of national income to about 60 per cent. Beijing's share of the gross national product has slipped from more than 30 per cent at the onset of reform in the early 1980s to 19 per cent. Internal projections say unless the trend is reversed, the centre's share may slip to 10 per cent by the end of the decade. Outlook, a mouthpiece of the party's Central Committee, says the target proportion is on a par with that in ''developed and developing countries''. The journal also reports that radical, instead of ''gradualist'' reforms, will be introduced at the plenum. Outlook confirms earlier reports that the ''financial contract system'' - whereby each province pays Beijing an agreed-upon level of revenue - will soon be abolished. It says there will be a ''unified tax rate'' for the entire country, implying, say Chinese economists, that coastal provinces, such as Guangdong and Hainan, may be hurt. Since the early 1980s, these areas, in particular Guangdong, have been paying much lower taxes and other contributions than ''wealthier'' provinces and cities. Outlook does not say whether the ambitious target can be reached within the 10-Year Economic Blueprint, which takes the country to the year 2000. Chinese sources said a ''ferocious debate'' would likely break out at the plenum and related national economic conferences on the amount of revenue that localities had to give to the centre. Coastal leaders have already said in private they would ''sabotage'' Beijing's efforts to claw back its lost financial power. Outlook quoted economists as saying that ''major breakthroughs'' in reform, particularly in the financial sector, would follow the plenum. Other liberalisation measures mentioned included transforming more state companies to joint-stock concerns and giving enterprises more control over their assets.