Federal drug enforcement agents have stepped up searches at the Mexican border partly because they are searching for 20 suspects in the Feb. 7 kidnaping of a veteran Drug Enforcement Administration agent, federal law enforcement officials said yesterday.

The searches also are intended to prod the Mexican government into stepping up its search efforts, which U.S. officials said are inadequate and apparently allowed four suspects to escape over the weekend in Mexico.

The searches coincide with new reports that Colombian drug czars have stepped up their war on U.S. DEA agents, including offering rewards of up to $350,000 to anyone who will kidnap top DEA officials, deputy DEA administrator John C. Lawn said yesterday.

Lawn said that he, DEA Administrator Francis M. Mullen Jr. and other high-level DEA officials are taking extra security precautions because of threats that began coming through informants and from intelligence sources in recent weeks.

The threats are taken seriously, Lawn said, because consistent information has come from Hispanic sources in California, Texas, New York and Florida.

Security at DEA offices around the country and at a number of U.S. courthouses and other offices was intensified this year after DEA learned that a three-man Colombian hit squad, hired by Colombian drug fugitive Carlos Lehder, had been dispatched to kidnap, torture and murder DEA agents.

Last Friday DEA asked the U.S. Customs Service to intensify its search procedures at the Mexican border to seek clues to the kidnaping of Enrique Camarena Salazar, a DEA agent who was grabbed by drug traffickers in Guadalajara.

Lawn said the Customs Service was asked to intensify its border efforts a day after DEA asked the Mexican Federal Judicial Police to conduct searches in Mexico for suspects in the Camarena case. The Mexican authorities did not carry out the searches until Sunday.

Lawn said DEA surveillance indicated that four men had left the search sites Saturday night before the Mexican search was effected.

In Eagle Pass, Tex., 18 Mexicans sought temporary refuge, fearing police reprisals after a violent political demonstration near the International Bridge on the U.S.-Mexico border, the Associated Press reported. More than 100 Mexicans fled across the bridge Sunday to the border checkpoint when gunshots injured up to four people, including three Mexican police officers, during a political rally in Piedras Negras. Most returned voluntarily yesterday.

Tension was running high in Piedras Negras yesterday as hundreds of plainclothes federal and state police officers roamed the streets keeping gatherings to a minimum. At least 10 American journalists were detained by Mexican authorities at various times for what officials said was illegal entry.