Rep. Ciro D. Rodriguez, who has alleged voting fraud during the Democratic primary he lost in March, is making a last-ditch effort to reclaim his seat.

Rodriguez plans to file a petition with the Texas Supreme Court on Monday appealing a recent ruling that let stand the 58-vote lead held by his opponent, Henry Cuellar.

"We recognize that it's a long shot, but we're optimistic," he told the San Antonio Express-News for Saturday's editions.

Rodriguez, a seven-year incumbent from San Antonio, led by 145 votes on primary election night. But Cuellar took the lead in a recount after more than 200 previously untallied ballots were discovered in Webb County, where he lives, and neighboring Zapata County.

Barring a successful challenge by the incumbent, Cuellar is set to oppose Republican nominee James F. Hopson in the November election in the heavily Democratic district.

Cuellar, a Laredo lawyer, said Friday he was "not at all" worried about Rodriguez's plans.

"The Election Code says specifically that you cannot appeal to the Supreme Court," he said. "I think it's now getting to the point where we're talking about being frivolous. Ciro needs to accept the fact that he lost and move on."

Rodriguez first sued in early April, alleging irregularities in the "casting, counting and recounting" of ballots. He amended the suit later that month, saying that some voters did not live in the district, whereas others gave false information to cast ballots.

Cuellar challenged the amended lawsuit, saying it raised new claims after the filing deadline.

A state district judge agreed. But a three-judge panel of the 4th Court of Appeals ruled 2 to 1 that Rodriguez had the right to question the legality of the votes.

The recent 5 to 2 vote by the full appeals court came along party lines, with the Republican majority saying that Rodriguez was trying to bring a different allegation to trial.

Rodriguez's petition says the appeals court violated civil procedure by requiring him to plead facts rather than broader causes of action, allowing the election to be settled on technicalities.

Lawyer Henry Cuellar leads the Democrat incumbent in the vote tally from the March primary. "We recognize that it's a long shot, but we're optimistic," said incumbent Rep. Ciro D. Rodriguez.