President Reagan's modest defense cuts will only slow down, not derail, his high speed rearmament effort, jubilant Pentagon officials said last night.

They saw no need to cancel any big weapons programs, to bring troops home from Europe or to deactivate any division as was forecast when the generals and admirals feared that Office of Management and Budget Director David A. Stockman would prevail over Defense Secretary Caspar W. Weinberger.

Most of the $13 billion Reagan wants to cut from the Pentagon spending account can be absorbed, officials said, by slowing the planned increase in Army strength and the stockpiling of ammunition abroad; retiring some Navy ships earlier and postponing construction of about 10 of them planned for the next five years, and reducing the volume of aircraft purchases for the next few years.

"It's a big victory for Weinberger," said an admiring fellow defense executive. He said Stockman pushed hard for cuts totaling about $30 billion for fiscal 1982, 1983 and 1984 and for slashing total obligational authority by $50 billion. The total obligational authority account includes money that is committed to defense contractors for future payment as well as those funds to be spent within a given year.

Pentagon officials, in explaining their reasons for being so upbeat about the Reagan decision, said it leaves unscathed the huge increases the administration made in President Carter's fiscal 1980 and 1981 budgets, while at the same time preserving most of the record high fiscal 1982 budget.

This budget, as submitted to Congress, calls for obligating $222 billion to defense.

The military services will get the detailed explanation of the president's decision tomorrow when the Defense Resources Board meets under the chairmanship of Weinberger or Deputy Defense Secretary Frank C. Carlucci. The services at that meeting will be asked to offer a list of reductions to achieve their share of the president's reductions.

Even though that list has not been drafted, knowledgeable defense officials said the cuts almost certainly will be absorbed in large measure through these economies:

Troops--Instead of increasing the size of the Army, Navy, Air Force and Marine Corps by 100,000 troops over the next five years, this buildup will be stretched out.

Ammunition--Instead of trying to pile up enough ammunition in Europe to fight for 60 days and enough in Southwest Asia to fight for 90 days, this stockpiling will be slowed down to save money immediately.

Navy ships--About five ships, rather than the 17 planned under the deeper cuts proposed by Stockman, will be retired early to save the millions of dollars it takes to keep them in service. In addition, about 10 warships from the 140 the Navy had hoped to build over the next five years will be deleted.

Officials said the Stockman goal would have required cutting 30 ships out of the building program.

However, officials foresee another fight between the Navy and the Marine Corps over what ships should be cut. The Navy is expected to target some of the ships the Marines want most, including amphibious "lift" vessels for taking Marines to distant trouble spots and high-speed cargo ships for supplying them there.

Aircraft--Purchases of the F15 fighter plane will be reduced for the next few years, with larger buys planned for 1985 and beyond.

Reserve forces--The administration has pledged a major effort to fill up the spaces in the reserve units designed to reinforce combat forces in a war. This buildup, along with modernizing the reserve forces by supplying them with modern aircraft, is expected to be slowed down.

The economies the Air Force will make to get under the ceiling as just lowered by the president will depend on imminent decisions on how many new bombers to buy and where to base the new MX land missile. Reagan is expected to commit himself to buying 100 updated versions of the B1 while pushing development of the Stealth aircraft designed to evade enemy radar defenses.

How fast he builds a new bomber fleet and where he puts the MX missile, and when, are the main forces shaping the Air Force budget for the next five years.

Weinberger, in successfully arguing against the deeper cuts sought by Stockman, stressed these points in White House sessions, officials said last night:

Slowing the rearmament effort significantly would undercut the effort to inspire NATO allies to increase military spending.

Going back to the traditional feast and famine cycle of purchasing weapons from defense contractors would end up costing more in the long run.

The president had described the threat as grave, the Congress had agreed and the Soviet military buildup shows no signs of the slackening that might have made deep cuts in defense spending safe at this time.