With the ghost of Mao Tse-tung finally laid to rest, China's Communist Party convened a National Congress today that is expected to ease out old-line political forces while setting a new ruling elite on the path of economic modernization and open-door foreign policy for the rest of the decade.

The congress is considered likely to be a milestone for putting the full weight of the party behind the reform programs devised in recent years by Vice Chairman Deng Xiaoping.

Deng, the wily, scientific socialist who is China's most influential politician, has been maneuvering since the last congress five years ago to reverse Mao's radicalization of Chinese society and to garner the organizational levers necessary to implement his own solutions for the nation's future.

At the congress' opening session, Deng delivered a keynote address restating his blueprint for "a clear-cut guiding ideology for socialist modernization." The speech reflected the careful blend of orthodoxy and innovation that has been the hallmark of his rule.

He pinpointed economic construction as the most compelling task for the rest of the 1980s and said it lies "at the core" of China's two other pressing objectives -- reunification of Taiwan and combating "hegemonism," which usually is a code word for Soviet adventurism.

China should learn from foreign countries, Deng said, but it will "build socialism with Chinese characteristics . . . and blaze a path" of its own, apparently with the mixture of central planning and limited capitalist incentives that characterizes current economic strategy.

In foreign policy, China will "unswervingly" keep open its door to the outside world -- a measure that already has enabled China to obtain know-how and technology from Japan and the West -- Deng said, but added that this openness stops at the point of importing decadent ideas and bourgeois life styles from abroad.

"We must proceed from China's realities," Deng told the congress at the Great Hall of the People. "China's affairs should be run in our own way and by our own efforts."

Although Deng's pragmatism has been the ruling philosophy of China for several years, he has had difficulty getting his programs implemented because of cautious or dissident party officials who cling to Mao's brand of political activism at home and self-reliance abroad.

Deng has managed to place his allies in the party's key administrative posts but is believed to have run into resistance from the legislative-executive body whose members were selected at the 1977 congress, when Maoism still was the prevailing ideology a year after his death.

After a series of complicated maneuvers, first to knock out his old-line foes, then to bypass them and finally to strike compromises, Deng has at last gained the political momentum to push through major organizational changes at this congress that should ensure smoother execution of his policies.

According to official reports and interviews with top party officials, this congress, the twelfth in party history, will adopt sweeping institutional reforms, including:

* Establishment of a central advisory commission, which will serve as a catch-all for the party's aged veterans, including Deng, who is 78. The panel will absorb almost all current Politburo members and play a supervisory role.

The commission provides a convenient way of retiring several conservative yet influential Politburo members who are believed to have bucked Deng on certain issues and who serve as rallying points for disgruntled party bureaucrats.

* Strengthening the Secretariat, which will inherit most of the Politburo's decision-making functions as well as handle the party's daily affairs. The body will be headed by Deng's two most important proteges -- party Chairman Hu Yaobang and Premier Zhao Ziyang.

Deng reconstituted the Secretariat in 1980, stocked it with his closest allies and gave it some of the Politburo's functions as a way of circumventing that conservative bastion. The congress intends to complete the process by making the Secretariat the party's chief executive branch.

* Abolishing the posts of party chairman and vice chairmen. This would prevent an elite corps of party officials from emerging as a rival to the Dengist Secretariat. It also would do away with a lineup of leaders Mao created in 1935 to solidify his stature as chief of the party.

This reform would cast the party into the Soviet model, which vests power in the Secretariat. According to the plan, Hu will become general secretary and Zhao -- now one of the six vice chairmen -- would assume another top Secretariat job. Four of the other vice chairmen would become advisers.

Only the fate of the sixth vice chairman, Hua Guofeng, is uncertain. Hua, who at 61 is too young to join the advisory council, was Mao's hand-picked successor as party chairman but lost out in a power struggle with Deng last year and surrendered his job to Hu.

What becomes of the Politburo in the new plan also remains unclear. If it is retained, the Politburo is likely to be altered by an entirely new Central Committee that will be cast in Deng's favor. The Central Committee, which is the party's legislative branch, will be elected by 1,700 delegates screened in advance by Deng forces at the provincial level.

Since emerging from being twice purged during the Cultural Revolution, Deng has built up an organizational base so solid that he is expected to step into semiretirement after this congress ratifies his program. Even if Deng withdraws from daily action, he would remain China's political doyen through the proteges he has tutored and put in important posts to shepherd China into the next decade.

"Gradually, Deng will fade from the scene," said an Asian diplomat, "but Dengism will last as long as his successors last."