DHAKA, Bangladesh (AP) _ One man was killed when a bomb he was making exploded in central Bangladesh and several opposition leaders were injured in clashes with police Monday, a day before scheduled opposition protests.

Demonstrators in Dhaka demanded the resignation of President Hussain Muhammad Ershad and threw stones and homemade bombs at police who responded with tear gas and baton charges.

Opposition leader Khaleda Zia and a half-dozen members of her Bangladesh Nationalist Party suffered minor injuries. One policeman was seen bleeding from the forehead.

Mrs. Zia and about 1,000 supporters defied a ban on public gatherings of more than five people shortly before sundown Monday when they marched down Topkhana Street and the fighting erupted.

The violence came on the eve of the opposition's call for a ''Dhaka Siege'' - a day of mass rallies and general strikes against the government.

Ershad, a former army general who took power in a bloodless coup in 1982 and was elected president last year, said he would not resign.

Speaking to foreign reporters less than three hours after the clashes, he said the Dhaka Siege had failed before it started.

Throughout the capital, riot police and paramilitary forces occupied major intersections.

Protesters set a jeep and a motocycle on fire in a separate demonstration in Dhaka's Gulistan commercial district, witnesses said. Police arrested some of the rioters, but the number was not known.

Dhaka University, a center of opposition politics, and all city colleges were shut down for one week from Sunday in a move to keep the students out of the scheduled protests.

A 30-year-old man was killed when a bomb he was making exploded in the port city of Chittagong, 165 miles southeast of Dhaka, police reported. They said two other people were injured by the bomb, which apparently was to be used in anti-government protests.

Traffic in Dhaka, a city of 4 million, was less than half the usual amount. Bus, train and ferry boat services have been curtailed, and many people have not returned from the countryside after last week's Moslem holiday marking the birth of the prophet Mohammed.

Reporters and other witnesses saw people in the Dhaka procession hurl stones and small bombs at police. Police retreated, regrouped and charged.

Mrs. Zia fell to the ground and later told a reporter: ''I was hit on my right leg by a tear gas canister.'' Party volunteers administered first aid at the scene.

A police official, speaking on condition of anonymity, said: ''Our action was purely in self-defense.''

Mrs. Zia is the widow of President Ziaur Rahman, who was assassinated in 1981. She has joined forces with another opposition leader, Sheik Hasina, in calling for Tuesday's mass protests against Ershad.

Hasina, head of the Awami League Party, is the daughter of another assassinated president, Sheik Mujibur Rahman, who was killed with his wife, three sons and a half-dozen other relatives in a 1975 coup.

Hasina also defied the ban on public gatherings Monday by driving through the city with a loud speaker and addressing small crowds that gathered along her path. Two trucks and a half-dozen jeeps loaded with police and paramilitary men followed her through the old city as she called on Ershad to resign.

After at least three such stops, police told her to go home. There was no violence.

Mrs. Zia and Hasina then met for 45 minutes and issued a statement urging people to join their Dhaka Siege on Tuesday and call for Ershad to resign.

''Why should I resign?'' Ershad asked when he met foreign reporters Monday night. ''I've been elected by the people.''

After ruling Bangladesh for five years as a military strongman, Ershad retired from the army in 1986 and was elected president, receiving what the government said was 73 percent of the votes.

''I'm not repressive,'' Ershad declared, dressed in light gray shirt and trousers and seated beside his country's red and green flag. ''I'm very accommodating. I'm very liberal.''

Ershad's Jatiya Party holds 213 of parliament's 330 seats, Hasina's Awami League has 79. The rest are scattered among Islamic, Communist and other small parties.

The protests were sparked by a Jatiya bill approved last July that permits military officers to hold seats on district government councils.

Ershad defended the measure, saying ''it is not actually a sort of army role'' in the government.

''Please do not compare our system with your system,'' he told the Western and Japanese reporters.

''This army fought for a political cause, a new state,'' he said, referring to the 1971 war in which Bangladesh, then known as East Pakistan, broke away from West Pakistan.

After the war, he said, the army felt neglected, so it was necessary ''to give them a role that they feel happy.''

Deputy Prime Minister and Interior Minister Abdul Matin told a separate news conference 6,000 police and paramilitary men were deployed in the capital. He said 1,146 people have been detained since Oct. 25 In connection with anti-Ershad demonstrations.

Mrs. Zia and Hasina say more than 6,000 have been detained.

Under Bangladeshi law, people can be detained for at least one month without trial for security reasons.