The laws, which laid down punishments for such crimes as rape, theft and adultery, were brought in 1979 by military ruler Mohammad Zia-ul-Haq and have drawn widespread criticism.
The proposed amendments include the removal of the need for a woman rape victim to produce four male witnesses. Another stipulates that sex with a girl under age of 16, with or without her consent, will be deemed as rape.
The Islamic laws, known as the Hudood Ordinances, set no age for sex with girls, saying only they should have reached puberty.
Law Minister Mohammad Wasi Zafar presented the bill to the lower house of parliament to loud protests with opposition Islamist members tearing up copies of the amendments.
"We reject outright this bill and will protest against it not only in parliament but outside as well," Maulana Fazal-ur-Rehman, opposition leader and secretary general of an alliance of Islamist parties, told parliament.
While conservatives oppose changes to the Islamic laws, rights activists have long demanded they should be repealed.
President Pervez Musharraf, who promotes an ideology of "enlightened moderation", has assured rights activists he would back any moves to amend or repeal the Islamic laws.
But with an election due by the end of next year, critics fear the government could lose some of its resolve should it need favors from the conservative, Islamist opposition.
Chuadhry Shujaat Hussain, president of the ruling Pakistan Muslim League party, told deputies any of the proposed amendments would be opposed if they were found to be un-Islamic.
Hina Jillani, a lawyer and human right activist, said she believed the changes would not go far enough.
Under the laws, a man and woman found guilty of having sex outside marriage could be sentenced to death by stoning or 100 lashes, while thieves would have their right hand amputated.
But those punishments have seldom been invoked, let alone carried out.
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