You remember ACE, that plucky little bulldozer the Army decided to buy some time ago to help solve a problem with its new M1 tank?

Well, it seems that ACE has a problem, too.

In just three months its price has gone up almost 50 percent, from $1.1 million per dozer last December to an estimated $1.6 million last week. And even at that price, the Army is not certain that the sole-source contractor, Pacific Car and Foundry Co. of Renton, Wash., will be able to build it, Army sources say.

ACE stands for Armored Combat Earthmover. The Army decided it needed the ACE to help the speedy M1 tank dig in when the M1 arrived wherever it wanted to be in battle. While the M1 is fast, its transmission is too delicate for clearing away battlefield debris or for simple, soft-earth moving. And while the Army's current bulldozer, the D7, is an unsurpassed digger, it is much too slow to keep up with the M1.

The new price increase is not the first for ACE. When the new bulldozer was first proposed in fiscal 1978, its cost was put at $200,000 each. Congress would not buy it. The next year the price had risen to $660,000. Again, Congress said no.

When the Army came back a third time last year, the cost per unit was put at about $1.1 million--$40.4 million for the first 36 machines. This time, Congress voted aye.

But no sooner had it done so than the Army began a design review, which was completed last week. That inquiry found, according to Army sources, that the ACE needed a new, more expensive cooling system and additional armor on the top to bring it up to the performance level it was described as having already attained. In addition, some parts have now risen in price.

Last week, the Army said its initial response to this would be to buy fewer vehicles. An Army official said that the fiscal 1982 money would be enough to buy only "25, or maybe even less." But, he added, the additional cost would eventually help bring the price down for future ACEs.

And then Defense Secretary Caspar W. Weinberger indicated in testimony before a House Appropriations subcommittee that the Army might even stop buying them altogether. After calling the ACE a "useful enough gadget," he said, "We are not going to purchase any more."

A spokesman in Weinberger's office, however, said the secretary meant to say only that there is no money for ACEs in the fiscal 1983 budget before Congress. As to the Army's future plans to buy more ACEs, the spokesman said that that "is what the service wants today . . . . Whether the secretary will approve it next year is an open-ended question."

The Army, meanwhile, has shifted ground on the M1-ACE combination in two others ways. First is the basic question of whether the M1 is too delicate to be fitted with a blade and do the simple scraping and soft-dirt moving that the older M60 tank still in service can.

When official testimony to this effect was first noted in a Washington Post report Feb. 9, Maj. Gen. James P. Maloney, director of Army weapons systems, wrote this newspaper that "our older tanks have such a blade, and so will the M1."

That contradicted what Army Chief of Staff Edward C. Meyer told Congress last year, which was that to put a blade on the M1, "You would have to use a different engine, different transmission."

Now, an Army spokesman has contradicted Maloney. The spokesman said last week that the Army plans only to "look at a device in August" that the Israelis have that could be attached to the M1 and serve as a blade.

The second problem has to do with how many ACEs the Army wants. Last year it said 1,300, but in a statement last week, the Army raised this to 1,400 to meet not only needs of the mobile regular forces but also the Rapid Deployment Force. In addition to all its other attributes, the Army says the ACE is the only bulldozer built that can be airdropped.