TRIPOLI, Libya (AP) -- A former U.S. congressman invited by Moammar Gadhafi arrived in Tripoli on Wednesday on a self-described private mission to urge the Libyan leader to step down as rebels and pro-government forces waged near stalemate battles.

Curt Weldon, a Pennsylvania Republican who has visited Libya twice before, said he leading a private delegation and had informed the White House and some members of Congress about his trip. He was in Libya's capital as a White House envoy, Chris Stevens, was meeting rebels in their de facto capital, Benghazi, to gauge their intentions and capabilities.

Gadhafi has been widely excluded from international efforts to broker a peace plan, with rebels insisting that his four-decade rule must end. Weldon would be one of the few high-profile Westerners to meet with Gadhafi since the rebellion began in February.

Weldon, who served two decades in Congress before losing his seat in 2006, was part of a bipartisan delegation that visited Libya in 2004 after Gadhafi agreed to abandon his nuclear program. The seven-member U.S. team included then-Sen. Joe Biden and included an address by Weldon to the Libyan Peoples' General Conference - a pro-Gadhafi forum - to urge greater understanding between Libya and the United States.

Weldon also visited Libya last year to study U.S. business opportunities.

"There is no question that America should play a critical role in helping the Libyans build a new government," Weldon wrote in an editorial published Tuesday in The New York Times. "Sadly, in the years since my first trip, Washington has squandered many opportunities to achieve that goal without bloodshed. And unless we begin to engage with the country's leaders - even those close to Col. Gadhafi - we may again lose our chance to help build a new Libya."

The rebels, aided by U.N.-authorized airstrikes intended to protect civilians from Gadhafi's forces, have maintained control of much of the eastern half of Libya since early in the uprising, while Gadhafi has clung to much of the west. Gadhafi has been putting out feelers for a cease-fire, but he refuses to step down.

Neither government forces nor the rebels have made any serious gains in recent days, and the conflict has shifted to smaller objectives on both sides, such as control of the key oil port of Brega.

Rebels have complained that NATO airstrikes come too slowly to seriously disrupt the pro-Gadhafi troops. But the French foreign minister, Alain Juppe, defended the air campaign, saying the missions are becoming more complicated as Gadhafi's forces position themselves in heavily populated civilian areas to make targeting difficult.

Juppe said airstrikes have destroyed most of Gadhafi's aircraft and armored vehicles, but that his troops are increasingly blending in with the rebels by using pickups and less sophisticated weapons similar to those the opposition uses.

"The military situation in the field is confused and uncertain and the risk of engulfing exists," he said in a radio interview.

In Misrata, the only major western Libyan city held by the rebels, Juppe said it has become more difficult for NATO to attack Gadhafi forces besieging the city because government troops have gotten closer to civilian populations.

A NATO spokeswoman also dismissed rebels' criticism, saying the number of airstrikes is increasing every day and that Misrata remains a priority of the air campaign.

Carmen Romero said the alliance flew 137 missions on Monday, 186 on Tuesday, and planned 198 on Wednesday.

But Romero also noted that NATO's priority is to avoid harming civilians and therefore "all operations are carried out in a very vigilant way."

"The ambition and precision of our strikes has not changed. The facts speak for themselves," Romero said in Brussels.

Rebels, meanwhile, were trying to sharpen their front-line forces.

Former Libyan military officers who have joined the opposition were trying to keep untrained fighters from advancing from the eastern gateway city of Ajdabiya toward Brega. But that was causing tensions within the rebel ranks.

"We only allow the people who have training to pass," said Walid al-Obeidi, a 25-year-old from nearby Benghazi who was a private in the Libyan army before defecting and was manning a checkpoint on the western outskirts of Ajdabiya.

Trained rebels flew through the checkpoints in pickups mounted with anti-aircraft weapons. One rebel in uniform got out with several grenades and military medals hanging from his vest and a Kalashnikov rifle flung across his shoulder. Others gathered around him, chanting: "God, Libya and freedom!"

But a scuffle broke out at the when one of the untrained fighters tried to go through toward the front line.

"Kill me here if you don't want to let me in! Let me in, I am trained to use weapons and mortars. My friends are there, let me in," he said, refusing to give his name to reporters. Guards in camouflage uniforms prevented him from passing while others tried to calm things down.

In another incident, a pickup truck carrying a group of ragtag rebels tried to go around the gate, but a rebel army officer fired warning shots in the air, then near the truck's tires to stop it.

Rebels who were not allowed to advance sat around, chanting anti-Gadhafi songs and clapping.

Raib bin Aruz, a 23-year-old student from the coastal town of Darna, said he hoped they would be allowed to go to the front in the afternoon, after an expected airstrike.

Saeed Imbarak, 43, a businessman, said he wanted to fight but didn't have a weapon.

"Gadhafi has weapons but we don't have enough. The Libyan people need more support from NATO. If we don't get it we expect a lot of massacres from Gadhafi. We expect him to take over all of Libya and to massacre all of us," he said.

In a step for the rebels toward getting more money for weapons and other needs, a Liberian-flagged oil tanker left the eastern port of Tobruk after loading up the rebels' first shipment of oil for export in nearly three weeks as part of a deal with Qatar.

The tanker can carry 1 million barrels of oil, less than the 1.6 million barrels Libya produced every day on average before the crisis.

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Associated Press writers Sebastian Abbot in Ajbadiya, Libya; Jenny Barchfield in Paris and Slobodan Lekic in Brussels contributed to this report.