WASHINGTON — Three Massachusetts congressmen are pushing back against a Pentagon proposal to shift nearly 40 percent of the U.S. Army’s 2012 budget for a satellite-enabled tactical communications network to other programs.

In a July 3 letter to the White House Office of Management and Budget, the lawmakers said the reprogramming request poses a “serious threat” to the Warfighter Information Network-Tactical (WIN-T) program. Congress appropriated $865.7 million in procurement funding  for the WIN-T program in 2012, but in a multiservice reprogramming request sent to Capitol Hill in June, the Defense Department proposed reallocating $334.6 million of that budget to other activities.

WIN-T is a multibillion-dollar program to field a high-speed, high-capacity backbone network that uses satellite and terrestrial-radio links to connect mobile tactical Army forces to command centers. General Dynamics C4 Systems, with major operations in Taunton, Mass., is prime contractor on the program, which has been plagued by cost overruns and undergone at least one restructuring.

Testing of the WIN-T network that had been planned for 2012 was delayed earlier this year so that it could be carried out “in conjunction with other programs,” the letter said. ”We agree that this slower rate of spending is appropriate given the delay,” the lawmakers wrote. “However, because the slow down is a result of a testing delay and not any flaw in the program, we are strongly opposed to transferring these funds to other programs with no assurance that a future Congress will restore them to WIN-T in a timely manner if and when the tests justify it.”

The letter to Jeffrey Zients, acting director of the Office of Management and Budget, was signed by Democratic Reps. Barney Frank, William Keating and James McGovern. The lawmakers said that while they are committed to reducing defense spending, U.S. forces must have the equipment needed to carry out their mission.

According to the reprogramming request, a copy of which was posted online by MilitaryTimes.com, a portion of the 2012 funding appropriated for WIN-T is available for other programs because of a decision to align “network on-the-move modernization efforts with platform modernization,” currently scheduled to occur between 2014 and 2017.

The WIN-T program, which includes transportable Ka- and Ku-band satellite communications terminals, is being rolled out in four increments.

The first increment is designed to provide Army forces with voice, data and video communications down to battalion-level units.

The second, expected to be fielded by October, is designed to provide a communications on-the-move network down to the company level, according to a July 9 Army press release.

A three-week initial operational test of the second increment was conducted in May, primarily at White Sands Missile Range, N.M., according to the press release. The test demonstrated the capabilities of the WIN-T equipment as it was moved and adjusted, according to the press release.

In submitting its 2012 budget request for WIN-T, the Army said the funding would be used for activities including procurement of all components needed to field 13 brigade combat teams by October. The reprogramming request said reduced funding in 2012 would not affect plans to field eight brigade combat teams in 2013 and would support deployment of another six in 2014.