TUCSON, Ariz. (AP) _ Mexican police crossed onto American soil and seized two men at gunpoint the same day the U.S. Supreme Court infuriated Mexico by saying U.S. agents could cross borders to nab fugitives, border officials say.

A Customs official said Thursday that such border crossings occur one or twice a year but aren't publicized.

Monday's alleged incursion into the southeastern Arizona town of Douglas followed the weekend seizure of a fugitive from U.S. courts in Mexico by private investigators from north of the border.

The Supreme Court ruled that in spite of an extradition treaty the United States was justified in the 1990 kidnapping of a Mexican physician wanted in the killing of a U.S. drug agent.

Mexico briefly suspended anti-drug cooperation after that ruling, and has protested the weekend seizure in the Mexican state of Sonora.

In the latest case, several men who appeared to be Mexican federal judicial police followed a van as it crossed into Douglas and stopped at a U.S. border checkpoint, said Fred Lawrence, district director for the U.S. Customs Service in Nogales.

Four American agents witnessed the incursion, ''two Customs, two Immigration,'' Lawrence said Thursday.

One of the apparent officers approached the van with a .45-caliber pistol, ordered two men out of the van and took them back across the border, Lawrence said.

A second man, with holstered pistol, unsuccessfully tried to get the van's driver to return with him, and a third man armed with an M-16 rifle stood nearby, Lawrence said.

He said the U.S. officers acted sensibly in not challenging the others because they were outgunned.

At least one of the armed Mexican men wore clothing with a judicial police emblem, U.S. agents said.

''This happens once or twice a year; this just isn't made public,'' Lawrence said. ''What happens is, when you're in a hot pursuit, your adrenalin's up. I suspect these officers didn't even realize they crossed the border.''

Lawrence declined to call the situation along the border tense.

''But officials on both sides of the border are trying to calm the waters,'' he said. ''The Mexican consul has been all over the radio stations across the border, assuring the people that these incidents are being looked into. I think that has a calming effect.''

The Arizona Daily Star in Tucson quoted Mexican police it didn't identify as denying the crossing took place.

The driver of the van, Pedro Samaniego Rodriguez, also disputed Lawrence. He said he and another man were taken in for questioning on the Mexican side of the border for an alleged traffic violation and were released.

Lawrence responded: ''Samaniego has to go back and forth across that border; he's gonna be careful what he says.''

In the weekend case, two men hired by a Tucson bail-bond agency brought a man identified by U.S. officials as Teodulo Romo-Lopez to the crossing at Naco, said port director Steve Rich. Mexican media identified the man as Teodulo Romulo Lopez; his citizenship was unclear.

Rich said the investigators told Customs agents they arrested Romulo Lopez in Mexico on a U.S. warrant for jumping bail. Agents verified the warrant and took the man into custody, Rich said.

''They went inside Mexican territory and abducted somebody,'' said Mexican Consul Emerenciano Rodriguez. He said the incident ''hurts very much our sovereignty and our feelings.''

Lopez was convicted in absentia in U.S. District Court in Tucson in November 1991 of possessing cocaine with intent to distribute. He had been arrested in May 1991 after he and others allegedly tried to sell 11 pounds of cocaine to undercover agents.

AAA Bail Bonds of Tucson had posted $75,000 bond for Romulo Lopez while he awaited trial, and that bond was forfeited when he failed to appear for trial, Assistant U.S. Attorney Daniel Knauss said.

Rich would not identify the private investigators who delivered Romulo Lopez to the Naco border crossing. AAA Bail Bonds manager Fred Luna said they were hired by his company's parent company, American Bonding Co. of Davenport, Iowa.

An employee at American Bonding said nobody was available to comment.