* Chinese president's speech well received by party heavyweights
* Xi could have new slogan included in party constitution
* Xi widely seen as strongest leader since Mao Zedong
* Congress to unveil new Politburo Standing Committee
* Multimedia coverage - http://reut.rs/2gN2YqY
BEIJING, Oct 19 (Reuters) - Top Chinese officials have praised President Xi Jinping's political ideology unveiled at a key Communist Party Congress, an indication that he could cement his power with his new slogan being incorporated into the party's constitution.
Xi opened the party's twice-a-decade congress on Wednesday with a speech pledging to build a "modern socialist country" for a "new era", and laid out a vision for a more prosperous China.
Whether Xi has his name crowned in the constitution during the congress will be a key measure of his status, its inclusion signalling his elevation to the level of previous leaders exemplified by Mao Zedong Thought and Deng Xiaoping Theory.
Zhang Dejiang, Yu Zhengsheng, and Liu Yunshan, all party officials on the elite 7-man Politburo Standing Committee, the apex of political power in China that is headed by Xi, praised "Xi Jinping Thought on Socialism with Chinese Characteristics for a New Era", according to the official Xinhua news agency.
"The Thought is the biggest highlight of the 19th National Congress of the Communist Party of China and a historic contribution to the party's development," Xinhua cited Zhang as saying in a congress panel on Wednesday.
In separate panels, Yu called it an important piece of the "system of theories" of Chinese socialism, and Liu said the "elevation of the Thought into the party's guiding principle" was of great significance, according to Xinhua.
Xi's immediate predecessors, Hu Jintao and Jiang Zemin, have had their ideological concepts enshrined in the constitution, but not their names.
Zhang, Yu, and Liu are all set to step down during the week-long congress, where the party will be given a new slate of top officials under Xi.
Already widely regarded as the strongest Chinese leader since Mao, the 64-year-old Xi has consolidated power swiftly since assuming the party leadership in 2012, locking up rivals for corruption, restructuring the military and asserting China's rising might.
The Central Committee, the largest of the party's elite ruling bodies, passed a proposal earlier in October to amend the constitution, although it didn't specify what would be included.
The party gave Xi the title of "core" leader a year ago, a significant strengthening of his position ahead of the congress.
Xi set bold long-term goals for China's development in his opening speech, envisioning it as a "basically" modernised socialist country by 2035, and a modern socialist "strong power" with leading influence on the world stage by 2050.
(Reporting by Michael Martina; Editing by Paul Tait)