Pakistan's chief economic planner hopes to develop his country into a breadbasket for the Middle East with the help of major American food processing companies.

Dr. Mahbub-ul-Haq, accompanying President Mohammad Zia-ul-Haq on a state visit here that began yesterday, said he is trying to get American agribusinesses interested in setting up operations in Pakistan aimed at supplying the Mideast market, which imports $17 billion a year worth of food.

While Pakistan has been promised more than $1.5 billion in annual sales for fruits, vegetables, poultry, livestock and flowers from Kuwait and Saudi Arabia, Haq said it needs help from experienced American companies to work with its farmers and supply them with proper seeds and poultry and livestock strains for export.

"We have supply constraints, not market constraints," said Haq, former policy planning director at the World Bank who returned to his native Pakistan earlier this year.

In a statement bound to delight the free enterprise beliefs of the Reagan administration, Haq said he wants help from American companies because his experience in the World Bank showed that Third World farmers learn better under the auspices of the private sector than government organizations. Moreover, he said the Pakistan government plans to loosen some of the administrative controls on its economy in a way that will make it easier for foreign firms to operate there.

He said the Pakistan government is aiming at a ten-fold increase in its food exports over the next five years -- something that needs a greater degree of organization than is available there.

As recently as 1979, Pakistan was forced to import food to feed its people. With good harvests over the past four years, though, Pakistan has turned into a food exporting nation.

Haq said Pakistan looks to foreign companies to supply, besides organizational skills, extension services to its farmers, and to ensure quality control of exports and assist with marketing.

He said Pakistan decided to concentrate on agricultural exports because newly industrialized nations are flooding the world with the kind of manufactured goods that his country could produce.

The oil-rich Gulf states of the Mideast, located a short boat trip and less than two hours by plane from Pakistan, comprise a food-deficient area that must import to eat. Much of the lamb eaten in the Arab sheikdoms, for example, comes from Australia and New Zealand, while the United States for years had been the major supplier of poultry. Now, however, Brazil has supplanted the United States in the Mideast poultry market.

As part of the government's new economic program, Haq said portions of 24.7 million acres of government-owned land presently lying fallow will be leased to the Pakistani private sector to be farmed in association with foreign assistance.

Some of that land could be used to raise livestock, especially sheep, for sale to the Mideast, where lamb is the staple meat in the diet.

Any move by Pakistan to increase its farm exports to the Mideast is likely to cut into America's agricultural sales in that region.