The U.S. Government Accountability Office (GAO) has further undermined the rationale for developing a new missile interceptor for installation in Poland and Romania. The Standard Missile 3 (SM-3) Block 2B is intended primarily to protect U.S. territory against Iranian long-range missiles lobbed over Europe. But the congressional watchdog agency, citing internal Defense Department analyses, casts doubt on the interceptor’s effectiveness in that role.

According to a GAO report released Feb. 11, SM-3 Block 2B interceptors launched from Romania would have difficulty engaging Iranian ICBMs launched at the United States because of unspecified “flight path” issues. Poland is a better option, but only if the interceptors can be launched early enough to hit targets in their boost phase, an engagement scenario that presents a whole new set of challenges. The best basing option is in the North Sea, but making the SM-3 Block 2B ship compatible could add significantly to its cost, the GAO said.

The report echoes one of the findings of a U.S. National Research Council missile defense study released last September. That report said the final phase of U.S. President Barack Obama’s so-called Phased Adaptive Approach to European defense, which features SM-3 Block 2B deployment, would do little to protect the eastern United States from Iranian missiles.

The SM-3 Block 2B would be the newest variant of the Raytheon-built SM-3 Block 1A, now operational aboard U.S. ships as a defense against medium-range missiles. But it would have significantly more capability than two other upgrades in the works, including the Block 2A being co-developed by Raytheon and Japan. Moreover, the Block 2B is the object of a three-way competition among Boeing, Lockheed Martin and Raytheon — all three were awarded design contracts worth over $40 million each in 2011 — suggesting it is much more than an incremental upgrade. Among the options being considered, for example, are liquid-fueled propulsion components, a complicating factor for sea basing.

Congress has doubts about the Phased Adaptive Approach in general and the SM-3 Block 2B in particular: Lawmakers provided only a fraction of what the Missile Defense Agency (MDA) requested for the program in 2012. Mr. Obama’s congressional critics often miss the mark in their eagerness to slam his missile defense strategy. But they’re on firmer ground in saying the Phased Adaptive Approach, at least with respect to U.S. territorial defense, was hastily approved.

According to the GAO, the MDA did not conduct a formal analysis of alternatives before initiating SM-3 Block 2B development — the reviews that exposed its limitations were conducted only after the fact. While noting that the MDA was not required to conduct the formal analysis due to certain “acquisition flexibilities,” the report said such assessments typically yield wiser procurement decisions.

The flexibilities accorded the MDA, presumably so it can field capabilities quickly, should themselves be reviewed. Fast-track acquisition programs have their place under certain circumstances, but as often as not they run into problems that lead to self-defeating delays and cost overruns.

The SM-3 Block 2B development program, meanwhile, has been dialed back due to funding constraints. The doubts raised by the National Research Council and now the GAO, coupled with the anemic budgets the Pentagon is likely to face in the upcoming years — with or without the looming sequester cuts — make it difficult to imagine there being room for the program in the Pentagon’s forthcoming budget request for 2014.