Peter A. DeFazio of Oregon bested Raúl M. Grijalva of Arizona in a hard-fought contest for the Democratic Steering and Policy Committee’s endorsement for the job of ranking member on the House Natural Resources Committee, setting up a final showdown before the full caucus on Thursday.

DeFazio triumphed 33-16 on Wednesday, but by capturing more than 14 votes, Grijalva won the right to ask all House Democrats to weigh in.

“There’s no guarantees there, but for the sake of participatory process, win or lose, I would prefer the full caucus to vote on it,” he said just before the vote.

The winner will succeed Edward J. Markey of Massachusetts — who was sworn in as a senator this week — as the party’s chief spokesman on the Natural Resources Committee.

Seniority worked to DeFazio’s advantage in the steering committee’s vote, and it is likely to give him an edge before the full caucus. He is now the most senior Democrat on the panel; Grijalva ranks sixth in seniority. Colleagues said that while both lawmakers have strong records on environmental and energy policy, the caucus generally should defer to those with more experience.

“I give seniority very high importance,” said Rep. Jerrold Nadler, D-N.Y., who plans to vote for DeFazio. “I would vote against the senior member only if there was something disqualifying.”

“Raúl’s a friend of mine, but Peter is masterful in terms of knowing those issues inside and out, and he’s been there over 20 years and carried a lot of water on a lot of complex issues,” added Oregon Rep. Earl Blumenauer.

Either contender would bring a Westerner’s perspective to a panel with jurisdiction over issues of importance to the region, including public lands, minerals and mining, oil and gas, and forestry.

In letters to colleagues trumpeting his environmental record, DeFazio has touted his 20-year record, citing a lifetime score of 89 percent from the League of Conservation Voters — which is the same as former Natural Resources Chairman George Miller, D-Calif. He would likely remain a steady Democratic voice against GOP efforts to open up more areas off the nation’s shores to oil and gas drilling. Forestry and fishing are important industries in DeFazio’s southern Oregon district.

During the contentious campaign, Grijalva pointed to his support from every Democrat in the Arizona, New Mexico and Texas delegations, along with that of the chairman of the Congressional Hispanic Caucus. He also boasted of endorsements from influential allies beyond Capitol Hill, who renewed their pledges to stand behind him on the eve of the caucus vote Thursday.

Brent Wilkes, vice chairman of the National Hispanic Leadership Agenda, said his coalition of nearly three dozen Latino civil rights and public policy organizations would be making calls to key lawmakers in the lead-up to the caucus meeting to shore up last-minute support.

The organization, along with other groups such as the League of United Latin American Citizens, hail Grijalva’s liberal politics — he is chairman of the Congressional Progressive Caucus — and stress the importance of having another ranking member at the Democratic leadership table who is a person of color and a staunch advocate for an immigration rewrite.

“You can’t just talk the talk if you really want to be the party that’s known for its achievements on diversity issues,” Wilkes said.

DeFazio voted in favor of a 2005 immigration overhaul bill backed by President George W. Bush, Grijalva’s advocates point out. At that time, he said on the floor that he was not enamored with the entire measure, which was never signed into law, but supported an opportunity to enhance border security.

The handful of outside groups supporting Grijalva are also worried about DeFazio’s vote against a 2009 bill to restrict greenhouse gas emissions. The “cap and trade” bill, which passed the House but never was taken up in the Senate, was authored by Markey and Rep. Henry A. Waxman, D-Calif.

While the race has aroused strong feelings among Democrats, Natural Resources Chairman Doc Hastings said he had no preference.

“I’ll work with both of them,” the Washington Republican said.