After again postponing a timetable for democratic elections, President Mohammed Zia ul-Haq said today that relations between Pakistan and the United States should be based on the principle of mutual strategic interests and not on dissimilarities of the forms of government in the two countries.

Zia, who leaves Sunday for a state visit to Washington, said in an interview at his martial-law administrative offices here that he thinks Pakistan can have an election in two or three years to replace martial law. But in any case, he said, the election would not precede a restructuring of the social order to conform to Islamic values and a stabilization of the economy.

Since seizing power in a 1979 coup and imposing martial law, Zia repeatedly has promised to hold elections. His most recent statement came in April when he said the mechanism for a national vote could be in place within nine to 11 months.

Apparently anticipating expressions of concern by the Reagan administration, which has embarked on a $3.2 billion military sales and economic aid package designed to shore up Pakistan as a front-line bulwark against Soviet expansionism in the Persian Gulf, Zia stressed that he has proven his ability to bring stability to Pakistan.

Zia said that in a few exceptional cases, relations between countries may be dependent upon similarities in their forms of government, but that the relations between the United States and Pakistan are "entirely dependent on the mutual interests of the two countries."

"So, at the present time, there are mutual interests of Pakistan and the United States that merge, in my opinion, to bring stability to this region," Zia said. "I do not boast, but I think I can rightly claim a little credit for bringing a little stability in this small island in this very turbulent region."

"We have no inhibitions of what I am and what I represent. I am a military man. I represent a military regime in Pakistan," Zia added. But he said he resented being portrayed as heading a "dictatorial regime" and added that he ordered the arrest of some opposition leaders earlier this week because they were trying to "pollute the minds of right-thinking, simple democratic citizens of the United States."

He said, "I cannot allow this to happen, not because I want to improve my image, but because I think they are damaging the cause of very friendly relations between two countries, Pakistan and the United States."

Opposition sources have reported that more than a dozen dissidents have been put under house arrest since the beginning of the week, mostly in the politically volatile Sind Province, which is a stronghold of the banned Pakistan People's Party. The party was founded by the former president Zulfiqar Ali Bhutto, who was executed by Zia's government.

Among those reportedly arrested is Mumtaz Ali Bhutto, a cousin of the former president, Ghulam Mustafe Jatoi, Sind People's Party leader, and Mairaj Mohammed Khan, secretary general of the Movement for the Restoration of Democracy, an alliance of opposition organizations that is demanding an end to martial law.

The sources expressed surprise over the wave of arrests, because the crackdown comes as political unrest has been minimal for several months and as the opposition is so fragmented and in disarray that it is virtually unnoticed. Zia has appeared recently to be the least vulnerable since he took control of the government.

With Pakistan's economy holding up relatively well and a wave of political violence during the summer subdued, the opposition appears more devoid of issues that could catch the public imagination and bring dissent to the streets.

An opposition activist in Lahore, traditionally a center of discontent, conceded in a recent interview that the Movement for the Restoration of Democracy had become ineffective. He blamed a lack of coordination and the absence of any issue other than martial law.

The timing was also surprising since Zia has been seeking to soften his image abroad and a wave of political detentions could hurt this effort at a critical point.

Zia appeared to have scored a public relations victory last month when he allowed Nusrat Bhutto, the president's widow, to leave the country for treatment of suspected lung cancer.

Zia said he had not ruled out the possibility of allowing political parties whenever elections are held, but he stressed that they could not be secular "because the fundamental Islamic principles must be inherent in any political party in Pakistan, because that is the ideology of Pakistan."

Zia also said that the intervention of 100,000 Soviet troops in Afghanistan had "fundamentally changed" the political equation in South Asia, and he conceded that Pakistan's relations with India had been altered as a result of the instability on the western border. But he said Pakistan and India still differ in their approaches to the Afghanistan question.

"We feel that if something wrong has happened, then everyone should shout the loudest," Zia said, noting that India had chosen a path of trying to persuade the Soviets to withdraw their troops. He added, "I've always doubted in my own mind what could be the mode of persuasion by a smaller country toward a superpower."

Zia declined to discuss his 45-minute talk with Soviet Communist Party leader Yuri Andropov when he attended Leonid Brezhnev's funeral in Moscow last month.

But Zia said he had detected a potential for a "freshness" in the new Soviet leadership and was willing to believe the Soviets' declared intention to seek a political solution and withdrawal from Afghanistan.

"Instead of having apprehensions and doubts, let us take the Soviet Union at its word," he said.

Zia said that he was encouraged by his meeting last month with Indian Prime Minister Indira Gandhi and that he planned to discuss the proposed nonaggression treaty with her when he returns to India in March for the summit conference of the Nonaligned Movement.

He said the principal obstacle to a treaty with India remains the disputed status of Kashmir, but that he is determined not to fight a third war over the issue.