MEXICO CITY (AP) — The party that ruled Mexico for seven decades appeared to be making a historic comeback in Sunday’s midterm congressional elections, scoring big with voters for the first time since it lost the presidency in 2000.

Early returns with about a fifth of the ballots counted showed the Institutional Revolutionary Party, or PRI, winning about 35 percent of votes for the lower house of Congress, against about 27 percent for President Felipe Calderon’s conservative National Action Party, PAN.

PAN national leader German Martinez acknowledged the PRI’s gains, but said they came at the expense of the leftist Democratic Revolution Party, Calderon’s archrival, as that party splintered and declined.

“The Institutional Revolutionary Party has won the status of the largest party in the lower house,” Martinez said, adding “we recognize and congratulate” the PRI on that.

The vote percentage does not translate exactly to the number of seats in the 500-member house, because of Mexico’s proportional representation system, and the PRI would not have an absolute majority of the kind it wielded up until 1997.

But the party was also leading in most of the six governor’s races at stake Sunday, including the border state of Nuevo Leon. The PRI was known during its 1929-2000 rule for a combination of heavy-handed political control and populist largesse.

Drug violence and the economic downturn weighed heavily in Sunday’s elections, seen by many as a referendum that could decide the future of Calderon’s anti-crime and economic policies.

The PAN had hoped the president’s nationwide crackdown on drug cartels would win it a bigger share of Congress, where it currently holds 206 spots.

But with the economy expected to contract 5.5 percent this year, its steepest downturn since the 1990s, the PRI could more than double its 106 seats.

Calderon’s party angered the PRI during the campaign by essentially accusing it of tolerating drug trafficking. The PRI could form an alliance with smaller parties to form a majority, and thus block Calderon’s efforts to reform police forces and give more police powers to 45,000 soldiers deployed to fight well-armed drug gangs.

“The fundamental problem is the lack of opportunities, jobs, education,” government worker Thelma Flores, 46, said as she waited to cast her ballot. “That’s what generates the other things, the criminality and organized crime. It’s because of a lack of opportunities2

Voters such as scriptwriter Fernando Orduna, 58, took part in a national movement that urged people to annul their votes or deface ballots to protest the largely government-funded political parties that have done little to break Mexico out of the doldrums.

The null vote was running at about 6.5 percent, much higher than in previous elections.