Hong Kong's legislature began a new session today, with the first elected members in more than 140 years of British colonial rule.

Twenty-four of 56 members of the Legislative Council were elected last month as part of Britain's plan to introduce democracy before the territory reverts to Chinese sovereignty in 1997.

The British are anxious to see Hong Kong's political community develop into a self-sustaining local government capable of holding its own under Peking's ultimate authority.

At stake are the preservation of existing freedoms for more than 5.5 million people and the continuing vitality of the world's third largest financial center, with foreign investment of more than $1.5 billion.

But Britain is faced with an unfamiliar complication: instead of passing the administration of Hong Kong to an independent government, they are passing it to a Communist power that has frequently indicated it does not favor a one-man, one-vote system for Hong Kong after 1997.

The last month has seen the emergence of friction at a grassroots level between incoming politicians and entrenched, if less official, powers.

Less than a month after the first territory-wide elections on Sept. 26, a brutal gang attack on an elected district official provoked fierce public debate over the dangers of political participation.

From the description of the attack, the police suspect the culprits were members of one of Hong Kong's "triads," a network of secret criminal societies that emerged in China during the late 18th century and has continued to dominate organized crime in overseas Chinese communities.

Ng Ming-yum, a 29-year-old schoolteacher, was attacked Oct. 10 by three men armed with metal water pipes and a knife as he and a colleague left their district office, according to police. Ng was hospitalized with serious facial and internal injuries.

No motive has been established and no arrests have been made. But community leaders have warned that whatever triggered the attack, one result may be to discourage others from political activity.

This attack, and warnings from resident Chinese Communist officials that further political developments must match Peking's blueprint for Hong Kong, have cast a shadow over the evolution of a political system here.

Some political optimists saw the 64 candidates running for 24 indirectly elected seats in the newly expanded 56-seat Legislative Council as a measure of how fast political attitudes can be awakened. For many years, the assumption that Hong Kong people were apolitical, seeking only to profit from the territory's impressive economic growth, had stood unchallenged.

Most of the successful candidates were political moderates, middle-class professionals or merchants with solid backgrounds in education, social or industrial work. Only a handful could be classified as belonging to the colony's social or financial elite. The council traditionally has been viewed as a rubber stamp, composed of civil servants and government appointees with close ties to the British establishment.

Under the new indirect electoral system, however, only 0.5 percent of the territory's population was eligible to vote for the council's elected seats.

Peking has guaranteed Britain that it will leave Hong Kong's capitalist system alone for 50 years after 1997. But many community activists and government officials fear that the absence of a democratic system would allow Communist interests to fill any power vacuum created by Britain's departure.

In the past two years, the number of known Chinese Communist Party cadres working in Hong Kong has increased sharply to up to 3,000, according to analysts.

The activities of the unofficial Chinese Communist headquarters here, the New China News Agency, have also been radically restructured to divide news operations from expanded propaganda activities aimed at neutral political interests.