Globe-trotting members of Congress reap a valuable fringe benefit they do not disclose: frequent-flier miles from trips they take at the expense of special interests or taxpayers.

It does not take long for the miles to add up to free personal travel or upgrades to first class.

"There's no question it's a definite benefit. I would call it a nice perk," said Rep. Ray LaHood (R-Ill.). He uses the frequent-flier miles for upgrades and personal free trips, such as travel to charity golf tournaments in Sun Valley, Idaho.

LaHood and his wife each accumulated about 13,500 miles this year from round-trip flights between Chicago and China financed by the Aspen Institute. LaHood was among a dozen lawmakers attending a conference on U.S.-China relations sponsored by the Washington-based think tank.

Lawmakers routinely travel at the invitation of private groups or on official trips for their congressional committees. Frequent-flier credits are not part of the information they must report about the trips or disclose on their annual ethics statement.

"Eventually a couple of trips is a free trip, right? So I suppose taking into account how rigid the normal rules are, this should technically be accounted for," said Kiran Pasricha, who heads the Washington office of the Confederation of Indian Industry. The pro-trade group, financed by Indian companies, flies several members of Congress to India each year.

Consumer Electronics Association spokesman Jeff Joseph, whose group pays for congressional visits to Las Vegas for its convention, said: "It does seem a bit strange that members have to report what really are nominal gifts . . . but not report frequent-flier miles."

Five-term Rep. Victor F. Snyder (D-Ark.) uses frequent-flier miles from official travel for seat upgrades on privately sponsored flights. Other lawmakers do the same, he said. "It is not a glamour life, traveling," Snyder said.

"If it's a requirement of employment to travel, I don't have a problem" keeping frequent-flier miles, he added.

Weekly flights home are a standard way for members to accumulate miles. A lawmaker flying weekly between Portland, Ore., and Washington would travel roughly 4,680 miles by air a week, or 243,360 a year. If all those yearly miles counted for United Airlines' standard awards program, they would be enough for six round-trip flights within the continental United States -- or four round-trip tickets to Hawaii.

Trips abroad sponsored by companies, labor unions and interest groups can yield thousands of miles. A visit to Sydney from Washington is nearly 20,000 miles round trip, and travel between Washington and Paris is about 7,700 miles round trip, for example.

"This is a gift that keeps on giving," said Kent Cooper, co-founder of the Web site PoliticalMoneyLine, which tracks congressional travel.

House and Senate rules let lawmakers decide individually whether their offices will allow personal use of frequent-flier miles or the credits some airlines offer instead of miles. All 535 members of Congress were surveyed to see how the miles and credits were used; fewer than 60 offices responded.

Of those responding, about two dozen acknowledged that the lawmaker and aides could add the miles and credits to their personal frequent-flier accounts. About three dozen lawmakers said they would reserve those credits earned from government travel for use on official trips or to let spouses and children accompany them on official travel.

Retired Sen. Alan Simpson (R-Wyo.) said he sees no problem with lawmakers keeping frequent-flier miles from government-financed travel, in part because other federal employees get to keep them and there is no conflict of interest with such trips. For travel paid by private groups, members of Congress should consider who is paying, Simpson said. "If you do the trip, then you must feel there is no conflict and then you keep the frequent-flier miles," he said.

American Airlines spokesman Tim Smith and Northwest spokesman Kurt Ebenhoch said members of Congress receive upgrades because they have earned them through frequent travel, not because of their office. Likewise, they said, frequent flying gives members of Congress access to the same special reservations lines as the airlines' best customers.

In the executive branch, Federal Election Commission employees are among workers who get to keep frequent-flier miles, although the government rather than the employee often selects the airline.

FEC Chairman Scott E. Thomas said he looked into setting up an FEC frequent-flier account so the commission could get the benefit of miles earned through employees' official travel but was told, "It's an administrative nightmare."

Thomas said it would be logical to require lawmakers and other federal employees to disclose the miles if they do add up to a substantial benefit -- and there was an objective way to calculate the value.

LaHood said he would not object to disclosing the miles.

Simpson thinks it would be a waste of time for members to report the miles, but he said that if failing to do so will expose Congress to ridicule, maybe they should disclose them. "If it's enough to create the concern in the American people that congresspeople again -- again -- are looking like boneheads, then why waste time on that one?" Simpson asked. "Just disclose it."

Rep. Ray LaHood (R-Ill.) uses frequent-flier miles collected from trips paid for by taxpayers and special interest groups for flight upgrades and personal trips.