Energy Secretary James R. Schlesinger was criticized yesterday by members of the Senate Energy and Natural Resources Committee for not being prepared to deal with the Iranian oil cutoff.

Ticking off a list of concerns in his opening statement, Sen. Henry Jackson (D-Wash.) scored the administration for not having a workable strategic petroleum reserve program, and chided Schlesinger for not providing Congress with a standby rationing plan.

Schlesinger again yesterday described the Iranian oil shutdown as "serious but not critical," saying that severe measures such as oil allocation or rationing would not be necessary unless the Iranian oil shutdown continues through the summer.

As a result of the Iranian oil shutdown, Schlesinger told the committee, the United States has been forced to go without about 500,000 barrels of oil a day, or about 1.5 percent of total energy consumption. So far, this has been made up by drawing on inventories and could, the energy secretary said, be made up by voluntary conservation measures, if necessary.

Nevertheless, Jackson, chairman of the Senate Energy Committee, said in his opening statement that the administration has lagged in its efforts to increase energy supplies, has "paid only lip service" to developing nuclear power, has been "less than decisive" about synthetic fuels programs, and has done a poor job of eliminating the west coast oil glut caused by new oil supplies from Alaska.

Jackson was joined by Sens. Dale Bumpers (D-Ark.) and Mark Hatfield (R-Ore.), who both pressed Schlesinger to send to Congress a standby gasoline rationing plan required by a 1975 law and now two years overdue.

"If we had a rationing plan today, we would be ready," Bumpers said.

Schlesinger told the committee that the Ford administration had sent a plan to Congress during its last weeks in office, but that the Ford plan had been withdrawn by President Carter. Since then, the Energy Department has prepared a gasoline rationing plan, and is expected to send it to Congress soon.

During the hearings yesterday, however, Schlesinger reiterated his position that gasoline rationing would only be "a last resort" in the event that the Iranian situation grew more severe.

Sen. Peter Domenici (R-N.M.) joined Jackson in saying the administration should place a higher priority on preparing a strategic petroleum reserve.

"I understand we are putting oil in the ground now that we can't get out," Domenici said.

Last month, DOE told Congress that contractors working on the oil reserves in Louisiana have yet to install pumps so oil stored there could be used in an emergency.

Schlesinger told the committee that the reserve, which now contains about 70 millon barrels, is running about a year beyond schedule. Last year, DOE told Congress it hoped to have 250 million barrels stored by the end of 1978. In 1977 Carter told Congress he wanted to expand the reserve to 1 billion barrels by the early 1980s.

"We expected to reach 150 million barrels by midsummer, but we won't because of the Iranian situation," Schlesinger said.

Schlesinger expressed a number of views on energy issues:

On oil price decontrol, which the president could announce next June, he said, "I cannot give you a definite statement." He also said that he would tell the committee by April 1 what the administration's intentions were.

On Alaskan oil swaps, which require congressional approval, he said that the administration might consider swaps with Mexico or Canada.

On Mexican oil and gas, he reiterated his position that the United States should burn off "the bubble of overdeliverability," as the domestic gas surplus is called, and only buy Mexican gas if Mexico lowers its prices.

Sen. Frank Church (D-Idaho) questioned Schlesinger's position, saying that buying Mexican oil and gas would allow the United States to use them in place of oil from the Organization of Oil Exporting Countries.