Mexican drug smugglers, gaining rapidly in wealth and power, soon could displace Colombia’s Cali cartel as leading supplier of the illicit U.S. market, the United States’ chief narcotics officer said Tuesday.

“If this happens, life as we know it in both the United States and Mexico will change dramatically,” Thomas A. Constantine, head of the U.S. Drug Enforcement Administration, told the Senate Foreign Relations Committee.

Constantine emphasized the growing importance to the American drug scene of Mexican-made methamphetamine, known as “speed” and sometimes called “poor man’s cocaine.”

Because of the flow from Mexico, the price of speed has plunged in California from $6,000 a pound to as low as $2,500 a pound, Constantine said. It has become the new drug of choice in some parts of the state.

Additionally, he said, Mexican groups trafficking in it are increasing their presence in the East, in farm regions and in suburbs of Georgia, Tennessee, Kentucky and the Carolinas.

And Constantine said Mexican manufacturers have even ventured abroad and bought ephedrine, an important narcotic for the manufacture of methamphetamine, from China, India, the Czech Republic and Switzerland.

“Unlike their previous role as middlemen moving cocaine and heroin, (as manufacturers) they can keep 100 percent of their profits from their methamphetamine sales,” Constantine said at a hearing on the extent of the Mexican drug menace.

His concern was echoed in a statement from Sen. Joseph R. Biden Jr., D-Del., a committee member and former chairman of the Senate’s Judiciary panel.

“The Colombian cartels may be on the way out, and concurrently the Mexican cartels may be rising to the top,” Biden said.

Robert S. Gelbard, assistant U.S. secretary of state for narcotics, emphasized that the smugglers’ connections within the governments of both Colombia and Mexico are central to their ability to operate freely.