The Carter administration is stepping up preparations to mine or blockade portions of the Persian Gulf in case the president wants to exercise either option, government sources said last night.

Navy specialists worked through the weekend on papers detailing for President Carter what those two military steps would entail.

Beyond those assessments, the Navy is sifting through its files of active and retired officers in a crash effort to find specialists in the tricky art of laying mines in distant waters such as the Persian Gulf.

The Navy already has drafted letters asking such retired specialists to return to active duty on a limited basis.Without a declaration of a national emergency, such requests must be invitations, rather than call-up orders.

The new talent hunt was triggered partly by the realization that the Navy was short of helicopter pilots experienced in air-dropping mines.

Either mining the sea lanes of the Persian Gulf or sealing up the waterway by a blockade would cripple Iran's economy. The gulf is the main lifeline for food and other supplies going into Iran, as well as the exit passage for Iranian oil, the country's main source of wealth.

From a diplomatic standpoint, either mining or blockading the gulf would carry the risk of the Iranian militants harming the 50 American hostages being held at gunpoint in Tehran.

From a military standpoint, there are also risks, but Carter could choose to take those risks if diplomacy and other economic pressures fail.

Defense Secretary Harold Brown said as much yesterday on the television program "Issues and Answers" (ABC, WJLA).

Asked about the prospects for a blockade, Brown said, "Specifically we cannont rule out the options of cutting off Iranian imports by one means or another," though he added that pressures by the international community were "much preferable."

Details on the mining and blockading options are being prepared for the president at Brown's direction and the White House's request.

Mines would give Carter some flexibility as to how and when he stopped ships from going in and out of the Persian Gulf shipping lanes.

Mines can be set to explode only under a certain size ship, and they also can be calibrated to go "live" after a certain number of ships have passed over them. The latter capability would allow Carter to give ships of all flags a certain time to leave the gulf.

Under one plan, the president would set a deadline for the release of the hostages after the mines were laid in the channels. He could couple such a demand with an offer to have the Navy clear away the mines as soon as the hostages were released.

The Navy could cover the entrance to the gulf with warships if the president opted for this military step. However, government officials explained, the real problem is not stopping a merchant ship but having enough air and sea power in the area if the Soviet Union should challenge the blockade.

Although the U.S. Navy has a sizable task force of warships in the Persian Gulf region now, military leaders said they would want to add to this power before setting up a blockade. This would require ordering into the area more ships from the Pacific fleet.

If the Soviet Union saw the United States massing warships and carrier-based fighter planes off Iran, sources said, it could respond by sending its own warships to the scene.

In that event, the Iranian crisis would have escalated to a direct superpower confrontation. Also, U.S. naval power in the Pacific would have been weakened, perhaps inviting a Soviet challange there.

Carter has discussed both the blockade and the mining options with Brown and other advisers. Presumably, he already has been acquainted with the risks and is interested in detailed plans, which are now being prepared as the impasse in the diplomatic situation with Iran countinues.

Besides Soviet ships, the United States must reckon with long-range Soviet aircraft already patrolling the sea lanes, such as the Backfire bomber.

The U.S. Navy mined the North Vietnamese harbor of Haiphong May 9, 1972 during the Vietnam war but the North Vietnamese had no significant navy or air force to threaten that operation.