RIYADH, SAUDI ARABIA, SEPT. 12 -- The full buildup of U.S. forces needed to combat the Iraqi threat to Saudi Arabia will not be completed for two more months, according to the top American military commander here.

Army Gen. H. Norman Schwarzkopf, chief of the U.S. Central Command, said in an interview that the buildup has been slowed about a week by breakdowns of ships carrying heavy combat equipment. Moreover, he said, the Air Force will be required to reduce its airlift of troops and equipment to the region in coming weeks because the operation has taxed aging transports so severely that many of their engines must be replaced.

Schwarzkopf said the buildup of U.S. forces on the Arabian Peninsula is running five to six days behind schedule because of sealift problems. He said U.S. forces are now adequate to provide credible defense of the kingdom but will be even stronger soon.

"Give me another couple of months, and we will surely have the forces on the ground that we need to defend Saudi Arabia against any attack they {the Iraqis} could possibly have," said the blunt-spoken general.

Schwarzkopf's comments came as Iran's spiritual leader, Ali Khamenei, called for a "holy war" to drive American forces from the gulf. His statement in Tehran, which boasted of the success of pro-Iranian suicide bombers in 1983 in driving the United States from Lebanon, was a chilling reminder of the vulnerability of U.S. forces in the gulf to terrorist attack. {Stories on Page A33.}

The U.S. buildup in the Middle East now totals about 143,000 troops, including sailors on naval ships, according to other military officials. More than 50,000 additional ground troops are scheduled to arrive in the coming weeks, officials said.

Based on Schwarzkopf's comments, it appears that the completion of the U.S. buildup will come about one month after the mid-October target reported by several congressman who were briefed earlier this month by top U.S. commanders in Saudi Arabia. Schwarzkopf indicated that these earlier predictions were overly optimistic and failed to take account of the sealift delay and other logistical problems.

Schwarzkopf said that while the massive movement of troops and hardware operated smoothly in the first weeks of the mission, less than one-third of the Army's heavy combat armor has arrived in Saudi Arabia. The military has been forced to contract slower ships to transport some tanks and heavy artillery because of mechanical problems with some of the Navy's eight fast sealift vessels.

"The good news is that at the most dangerous time, everything went great," Schwarzkopf said. "The bad news is it has slowed up, but it doesn't matter as much as it did before."

Schwarzkopf said air transport flights into the Middle East region have dropped from an average of 80 a day to about 70 a day in the last week. He said that number will drop further in about two weeks, when the Air Force begins massive overhauls and maintenance of its transport planes, which have been flown hard in the past four weeks. The four-star general also said the flights will begin tapering off as more equipment continues to arrive by sea.

The Army has not finished deploying the first of three heavy mechanized divisions into Saudi Arabia, officials said. About half of the 50,000 Marine forces assigned to region have arrived, with a large amphibious assault group scheduled to arrive in the Persian Gulf off the coast of Saudi Arabia within the next several days. Those amphibious units, which could be used in a beach assault into occupied Kuwait, are likely to remain offshore, aboard their ships, Marine officials said.

Air Force officials, who have amassed hundreds of fighter and attack planes throughout the Arabian Peninsula, said most of the remaining units they plan to deploy will be in place within two weeks. Most of the military's special operations units assigned to the region, including Army and Air Force special forces and Navy SEALs (sea-air-land) also will be in place within two weeks, officials said.

Military commanders in all of the services said that they are already grappling with serious overcrowding problems at sleeping areas for troops and that they expect the problems to become more acute as additional forces arrive.

American commanders throughout Saudi Arabia also said the operation has been slowed by difficulties in matching up troops, who are flown here, with their equipment, which is arriving by sea. Officials said it has taken longer than expected to organize military units and dispatch them to their defensive posts in the desert.

"Certainly it's not perfect," said Lt. Gen. John J. Yeosock, commander of Army forces here. "But our projection of people as well as things has exceeded any other comparable period in history."

Schwarzkopf said the operation has begun to shift from emphasis on organizing troops and coordinating basic logistical needs with the Saudi military to considering policies for rotating troops back to the United States and discussing detailed combat tactics with the Saudis.

Some Army officials said they are considering returning some elements of the 82nd Airborne Division to the United States after more of the armored units arrive. The Air Force already is planning to replace some of its fighter squadrons with fresh units from the United States, officials said.

Schwarzkopf said he expects the number of Saudi and other Arab forces to equal the strength of U.S. and other Western troops when the buildup is complete.