COLOMBO, SRI LANKA, AUG. 18 -- Assassins launched a gun and grenade attack in Parliament today, killing a lawmaker and wounding the prime minister, five of his Cabinet and about a dozen other people but failing to hit Sri Lanka's president.

The attack, on a meeting of the ruling party at the Parliament complex in Sri Jayewardenapura 10 miles from the city center, took place three weeks after the president, Junius Jayewardene, signed an accord with Indian Prime Minister Rajiv Gandhi to end a four-year-old rebellion by minority Tamils.

A man identifying himself as a member of the Patriotic People's Movement, a previously unknown group, telephoned a British radio reporter in Colombo to claim responsibility for the attack.

He said the group was against the July 29 pact between Jayewardene and Gandhi and also opposed the presence of 7,000 Indian troops who have been stationed in the northern and eastern provinces to enforce the accord.

Sections of the majority Sinhalese people in the south of this island nation have protested violently against the pact as a sellout to the Tamils, who live mainly in the north and east.

The degree of resentment against the agreement was dramatically displayed when a Sri Lankan sailor, a member of an honor guard, assaulted Gandhi with his rifle butt hours after the prime minister signed the pact.

The government said a shot fired at Jayewardene, who was chairing today's party meeting, hit a clerk in the spine. The clerk was presenting papers for the signature of Prime Minister Ranasinghe Premadasa, seated next to Jayewardene.

After the shot rang out, two grenades were flung at the president, a spokesman said. One fell on the table at which Jayewardene was seated, bounced to the floor and exploded in front of National Security Minister Lalith Athulathmudali.

The second grenade also went off and wounded four other Cabinet ministers and 13 more members of the ruling United National Party.

Jayewardene was taken to his car by some members of Parliament and security men, while the wounded were rushed to hospitals.

Premadasa was wounded in the leg and Athulathmudali was operated on for abdominal injuries.

Hospital sources said Keerthie Chandradasa Abeywickrema, who represented a southern consitutency, Deniyaya, died of his injuries on an operating table.

Police said no arrests had been made.

In a radio broadcast soon after the attack, Jayewardene said it was an attempt to destroy the parliamentary democratic system of the island.

He said the government had been able to stop Tamil guerrilla violence in the north and east following last month's pact. "But, the terrorists living in the south are continuing their activities," he said.

Jayewardene did not identify any group. He had on earlier occasions accused an outlawed southern left-wing group, the Janatha Vimukthi Peramuna, of involvement in the violent protests against the pact that killed 74 people.

"We seek the aid of all those who are interested in the freedom, the democracy, the integrity and the unity of the country, to join hands with the government to oppose this sinister attempt," Jayewardene said.

"We intend to carry on our work irrespective of evil forces that are ganging up against us," he added.

The attack was made despite tight security clamped on the city and its outskirts since morning as Parliament was due to meet today for the first time since the pact was signed.

Parliament's public gallery had been closed and police and soldiers were guarding key points around the Parliament building.

Officials said the security measures had been enforced to prevent trouble even though the pact was not due to be discussed today, in parliament according to the agenda.