The joint effort by a Dutch insurance group and Mexico's largest financial group to cash in on an underdeveloped insurance market in Mexico was affirmed enthusiastically Thursday by the Dutch half of the alliance.

"They are the leading bank and we are a leading insurance company, so it's the best combination," said Cees Brink, group secretary of Aegon Insurance Group of the Hague, regarding its partnership with Grupo Financiero Banamex- Accival (Banacci).Aegon on Tuesday formalized its commitment to buying a 49 percent stake for $383 million in a new life insurer, Seguros Banamex, which will change its name to Seguros Banamex Aegon.

Asked why it had chosen Banamex to invest in over the other insurance prospects in Mexico - including Aseguradora Mexicana, which is being offered for sale by the Mexican government - Mr. Brink said, "Aegon and Banamex have chosen each other. Banacci has a large branch network in Mexico, and Aegon is the largest non-U.S. insurer in the United States."

Aegon has paid $109 million up front in the culmination of a preliminary agreement, announced last November, to acquire a substantial stake in the insurance arm that Banacci was intending to establish.

The devaluation of the Mexican peso and general economic distress that ensued halted the transaction, but the Mexican insurance market - which is markedly underdeveloped, even by Latin American standards - was considered too great an opportunity to miss. Seguros Banamex was set up in April with a capitalization of 40 million pesos ($6.28 million), and has gradually been taking over the life-insurance policies linked to mortgages issued by the parent bank.

"It is the opinion of both Banacci and Aegon that the success of Mexico's drastic economic adjustment program, in place since January 1995, in terms of restoring the stability of the main financial variables and setting the conditions for renewed future growth, now provides a solid framework within which to redefine and formalize their agreement," a joint statement said.

The move, announced by Banacci and Aegon as "the formation of a strategic alliance for the insurance business in Mexico," involves Aegon paying equity to Banacci that will be adjusted in either direction, based on the venture's growth and profitability over the next 10 years.

The initial equity consideration is $167 million. The $58 million remaining after the $109 million payment will be paid at various times throughout the 10 years. In addition, Aegon will acquire $216 million of 10-year debentures issued by Banco Nacional de Mexico (Banamex).