Sri Lankan President J. R. Jayewardene outlined broad-gauged proposals for political reform today, opening a new effort to halt the ethnic violence that has killed or injured an estimated 2,500 people in this South Asian island nation this year.

Underscoring the growing violence, national defense officials said today that bombs, apparently set off by Tamil militants overnight, killed 16 persons and injured 56, many of them seriously. Most of the victims were civilians. Three Tamil militants were reported killed and five police officers wounded in a separate clash.

The bombs went off in the troubled northern and eastern provinces of the country only hours before Jayewardene met with representatives of eight of the country's political parties to outline proposals designed to resolve differences that have led to wide suspicion and violence between Sri Lanka's Sinhalese and Tamil populations.

Security police also reported that one small bomb went off in the capital this evening, injuring one person.

The president called the proposals a "new chapter" in the country's political process and urged that "past suspicions be forgotten to secure a better future for all."

Under the proposals, Sri Lanka's highly centralized form of government, which leaves most political, judicial and police powers in the hands of the 74 percent majority Buddhist Sinhalese population, would be changed to allow for a large measure of provincial control. This would give the Tamils, who are predominantly Hindu and make up 18 percent of the population of 16 million, a greater voice in regions where they live.

The Tamils have long accused the Sinhalese majority of discriminating in employment and in higher education and of suppressing the Tamil language.

As indicated by the bombings this morning and by widespread government security sweeps yesterday that led to the detention of a reported 400 Tamils, the political process is likely to be a difficult one given the widespread mutual distrust that has become deeply ingrained in the last three years of ethnic violence that borders on civil war.

The mainstream Tamil party, the Tamil United Liberation Front, refused from its exile headquarters in Madras, India, to attend today's meeting.

On the other side of the spectrum, Jayewardene's political foe within the Sinhalese community, former prime minister Sirimavo Bandaranaike, also boycotted the so-called all-parties conference, although she and representatives of her Sri Lankan Freedom Party met separately with the president.

Not present but playing a large role in the Sri Lankan political drama is the government of Indian Prime Minister Rajiv Gandhi.

India's southern Tamil Nadu state is separated from predominantly Tamil northern Sri Lanka by only about 18 miles of water. It has provided an exile home for Sri Lankan Tamil political leaders and refuge for an estimated 125,000 Tamils who have fled this country. Their presence bolsters allegations of widespread abuses by Sri Lankan security forces; more important, there is increasing evidence that Tamil militant groups have found safe haven in southern India bases, although the Indian government continues publicly to deny their presence.

Sources familiar with the Indian position in the current round of talks said today that New Delhi had summoned Tamil leaders for discussions in the Indian capital to explain behind-the-scenes negotiations that have taken place between Indian and Sri Lankan representatives over the past several weeks.

There was a clear implication that Delhi is prepared to press both sides hard for a political solution.

"Everyone, including New Delhi, is getting tired of the violence and wants to bring it to a halt," said one knowledgeable source, adding that there were indications the Gandhi government is prepared to crack down on Tamil guerrillas if the other parties take up the political process.

With some 5,000 to 7,000 armed men in the field, the attitude of the Tamil forces becomes crucial and there have been no indications of any willingness on their part to compromise.

One guerrilla leader in the northern stronghold of Jaffna told a British Broadcasting Corp. correspondent within the past week that the main guerrilla group, the Liberation Tigers of Tamil Eelam wants "nothing less than a totally independent Tamil state."

That group has all but forced the Sri Lankan Army out of the Tamil-dominated Jaffna peninsula and is attempting to push its way south. In the divided Eastern province, centered on the cities of Trincomalee and Batticaloa, something of a standoff has developed between the Army and guerrilla forces.

Following today's opening session, representatives of the various political parties are expected to discuss the details of the government's plan and reconvene sometime in July. Proposals for giving widespread control to elected provincial assemblies over sensitive issues like police, courts and land distribution are expected to be hotly debated.

Jayewardene's United National Party enjoys almost complete control of the Parliament and could easily push through the constitutional changes necessary to implement the political changes outlined today. But unless he gains the support of, or neutralizes, Bandaranaike's party, political observers say he will be running the considerable risk of a clash with the powerful Buddhist clergy, who largely have opposed concessions to the Tamils.

Even if Jayewardene succeeds in a process that is expected to last at least through the summer, there still is the question of whether the Tamil militants can be brought under control.