A new sports bra that counts heartbeats is causing a Christmas stir.

The bra, introduced last week, is the first consumer product to be based on an electronic interaction between a textile and its wearer. A special conductive fabric in the chest band, when it’s wet, picks up the heart’s electrical pulse and radios it to a digital readout wristwatch via a tiny transmitter in the bra.

Such “smart fabrics” are the next big thing in so many fields that some analysts go so far as to predict that they’ll change the world as dramatically as the Internet did.

“The applications are limitless, and they’re for everybody,” said Spyros Photopoulos, an analyst at Venture Development Corp., a technology market-research firm in Natick, Mass.

Photopoulos says that hundreds of companies, foreign and domestic, are chasing the potential of miniaturized electronics that people can wear.

A medical application for a smart shirt that monitors heart rate and respiration continuously with the help of sensors and wiring woven into its spandex already has been approved by the Food and Drug Administration. The shirt, made by VivoMetrics of Ventura, Calif., currently is used mainly to unobtrusively monitor patients with a respiratory disturbance called sleep apnea.

A future variant worn by chronically ill patients at home could extend their lives by enabling doctors to better monitor their health and to intervene faster when trouble arises. Robert Litan, a public policy economist, estimated earlier this month that monitoring 4 million chronically ill Medicare patients better at home also could save $30 billion a year in reduced hospitalization, emergency room and doctor costs.

Many researchers expect the deep-pocketed Pentagon to back the development of smart fabrics, much as it did for computers and the Internet. The Institute for Soldier Nanotechnologies at the Massachusetts Institute of Technology, which the Army launched in 2002 with $50 million, is the biggest visible step in that direction. It’s developing battlefield garb that would be woven with miniaturized electronics that would report a soldier’s location and vital signs to commanders and medics.

Fast, “point of need” medical treatment is the vision. Sensors in the uniform would detect fractures, uncontrolled bleeding or the soldier’s collapse, helping medics to treat first those who need help the most. In the more distant future, the sensors could trigger the battle garb’s synthetic polymers, substances that alter their molecular shape when magnetized, heated, shocked or impacted. The polymers’ new forms would stiffen, tighten or pulse the fabric to provide the injured soldier with a splint, tourniquet or cardiopulmonary resuscitation.

Such capacities could be available in smart fabrics “within a couple of decades,” according to MIT professor Ned Thomas, the head of the nanotechnologies institute and of MIT’s materials science and engineering department. That may seem far away, but it’s faster than the evolution of the modern computer from the first miniaturizing transistor in the 1950s, said professor Mahmoud El-Sherif, a researcher in flexible electronics who’s on leave from Drexel University in Philadelphia.

El-Sherif has worked with the military on smart parachutes that adjust their shape to their weight of their load and on fabrics that detect and respond to toxic chemicals. He’s also working on flexible electronics, essentially computer circuits that can be printed onto fabrics or screens.

For now, industrial clients are keen simply for fabrics that respond to temperature changes, according to Julie Case, the technical services director at Industrial Fabrics Association International in Roseville, Minn. While some combinations of computers and fabrics “sound a little Star Trek-y,” she said, the association’s members are looking for products such as pipe wraps whose insulating properties adjust to temperature changes or suits for firefighters that do the same.

The sports bra, made by Textronics Inc., of Wilmington, Del., is a pioneer among consumer applications, industry analyst Photopoulos said. Its main innovation is the conductive fabric: The wrist monitors are widely sold separately, and so is the transmitter, which is the size of a small matchbox and uses radio waves to relay the impulses to the monitor. The transmitter snaps into a pocket in the front of the bra – and out for machine washing.

The bra, transmitter and monitor are available only online from www.NuMetrex.com and cost $115 to $145 as a set. The bra alone is $45. A T-shirt version for men is planned next year.