WASHINGTON — Going to bat for confused passengers, the government is proposing that airlines be required to disclose fees for basic items like checked bags, assigned seats and carry-on bags so consumers know the true cost of flying.Under regulations proposed Wednesday by the Transportation Department, detailed fee information — including for a first and second checked bag — would have to be provided wherever passengers buy tickets, whether online, on the phone or in person. Any frequent-flier privileges would be factored into the price.Now, airlines are required to disclose only bag fees, and even then they don’t have to provide an exact price. Some provide a wide range of possible fees in complex charts. The rule would also require airlines to share fee information with travel agents and online ticketing services, which account for about 60 percent of ticket sales. Fee information is now usually available only through airlines.The rule doesn’t cover fees for early boarding, curbside check-in and other services. The government also wants to expand its definition of a “ticket agent” so that consumer regulations like the fee disclosure requirement apply to online flight search tools like Kayak.com and Google’s Flight Search, even though they don’t actually sell tickets. Many consumers cannot determine the true cost of a ticket because fees are often hard to find or decipher, the government says. “A customer can buy a ticket for $200 and find themselves with a hidden $100 baggage fee, and they might have turned down a $250 ticket with no baggage fee, but the customer was never able to make that choice,” Transportation Secretary Anthony Foxx said in an interview. “The more you arm the consumer with information, the better the consumer’s position to make choices,” Foxx said. The public has 90 days to comment on the proposal. Foxx said he hopes the rule will become final within a year. The effort is partly a response to changes in airline industry business strategy since 2008, when carriers started taking services out of the price of tickets, beginning with checked bags. More recently, some airlines have begun offering consumers not only a stripped-down “base” airfare but also a choice of several packages with some of the once-free services added back into the cost of a ticket, but at higher prices. With packages and a la carte fees multiplying, comparison-shopping for airfares is becoming harder, consumer advocates say. A trade association for the airline industry said the “proposal overreaches and limits how free markets work,” predicting “negative consequences.” “The government does not prescriptively tell other industries — hotels, computer makers, rental car companies — how they should sell their products, and we believe consumers are best served when the companies they do business with are able to tailor products and services to their customers,” Airlines for America said in a statement. But Charlie Leocha, who lobbies for passenger rights on behalf of the Consumer Travel Alliance, welcomed the proposal. “We are getting most of what consumers have been requesting for more than five years,” he said. The proposal would also: • Require large travel agencies to adopt “minimum customer service standards,” such as responding promptly to customer complaints and providing an option to hold a reservation at the quoted fare without payment for 24 hours if made more than a week ahead of the flight.• Require airlines and ticket agents to disclose whether the ticket being sold is for a flight operated by another carrier under a partnership arrangement. For example, United Airlines sells tickets for flights operated as “United Express” by several regional airlines. But the planes and crews belong to the regional carrier. • Prohibit “unfair and deceptive” practices by airfare search tools, such as ranking flights by some airlines ahead of others without disclosing that bias to consumers. The proposed rules are the Obama administration’s third wave of consumer protections for airline passengers. The effort began with a ban on “tarmac strandings,” in which passengers were cooped up in planes for hours, sometimes in miserable conditions. Other regulations include tougher requirements for compensating passengers denied boarding because of overbooking and a requirement that airlines, travel agents and online ticketing sites display full airfares, including taxes and government fees, more prominently than base airfares. Previously, airlines often advertised base fares and buried mention of taxes and government fees — typically about 20 percent of the ticket price — in fine print.