(MONEY Magazine) – An airline war suddenly erupted in March. Overnight, newspaper ads fairly shrieked with come-ons: ROUND TRIP TO LONDON FOR $318 . . . DENVER TO HONOLULU FOR $446. An industry watchdog, editor Ed Perkins at Consumer Reports Travel Letter, noted, ''You'd have to go back to the el cheapos of the late '50s to find values like that.'' But as quickly as it began, the war ended. So if you missed out on the great air-fare sale that disappeared on April 8, or if you didn't get one of British Airways' 50,000 freebie seats on April 23, what do you do now? Basically, you can make your own breaks this summer. Customize your vacation plans by taking advantage of limited-offer fares as well as the new wave of travel packages, perks and upgrades. Also, track down a savvy travel agent. His advice will pay off. How else can you find this season's deals? Here's help:

Will there be more promotional fares this year? Probably. But don't wait for another cutthroat fare war. ''There's lots of apprehension and heartburn in the industry,'' says Robert Harrell of the Airfare Management Unit of American Express Travel. ''You may have missed the big sale, but there will be little sales throughout the year.'' Tom Parsons of Best Fares, an air-fare-discount magazine ($58 a year; 800-635-3033), suggests you get an edge by joining all the frequent-flier clubs you can to collect valuable discount coupons, like Northwest's recent $118 San Francisco to Dallas round-trip deal. ''This is the year of the bargain,'' predicts Parsons.

With the airlines advertising so aggressively, do I need a travel agent? You definitely do. Agencies like American Express or Carlson, which claims a 6% domestic market share, often have more clout with airlines, hotels and, particularly, cruise lines. Whether the agency is large or not, however, a travel agent's knowledge and contacts get you lower rates and a better choice in packages. Agents can also ferret out the best fares in a fraction of the time you can. ''The more complicated fares become,'' explains Alan Fredericks, editor of Travel Weekly, an industry magazine, ''the more you need an agent's computerized fare-search capability.'' With systems such as Sabre or Apollo, agents can instantly punch up and compare fares and schedules of several airlines. But no matter how whizzy the technology, there's nothing like hands-on. Dan Bohan at Omega Travel, which has 700 agents nationwide, points out that ''there's always an inventory gap.'' He explains that ''a good agency with longtime relationships can call the airline sales desk and ask them to change an unsold seat from one fare to another.'' To really get the lowest fare, let your travel agent know you're willing to make trade-offs, suggests American Express' Robert Harrell: ''Be prepared to leave from one airport and return to another, or travel by a circuitous route.''

Is there any way to clinch an advertised low fare? All you can do is try. Dial the airline -- quick -- and stay poised over the redial button. Maybe you'll get lucky. Most of the time, only a small percentage of a flight's seats are set aside for advertised low fares, and airlines run out fast. ''The airlines have a terrible habit of fraudulently advertising low fares they know they can't fulfill,'' charges Mark Green, commissioner of New York City's Department of Consumer Affairs. Green's claims are based on a report his office published last year called Flights of Fancy: Deception in Airfare Ads. (Also, the U.S. Transportation Department has a complaint number: 202-366-2220.) Again, hard-working travel agents who monitor reservations systems around the clock can help. But ''be hard-nosed,'' stresses Ed Perkins. ''Make it clear to the travel agent that the airline advertised this fare, and you want it.''

With fares slip-sliding so much, is it worth checking with consolidators? Yes, because it's difficult to get a low, short-term fare. And you'll get the next best price from major airline consolidators, such as UniTravel (800-325-2222), Sunline Express (800-877-2111) or Council Charter (800-223-7402), which sell international and domestic tickets at wholesale prices both to travel agents and directly to consumers. ''My cost is higher than what they were selling tickets for in March and April,'' says an exasperated David Kols at the St. Louis-based UniTravel. ''Our business was down from 5,000 calls a day to maybe 2,000. But still, people called wanting cheap seats, and the airlines didn't have any more.'' Consolidators may not offer $318 round trips to London this summer, but their $600 or so fares to Europe will be the lowest around.

Is it wise to buy tickets on airlines in Chapter 11? Speaking specifically about Pan Am, Continental and Midway, Ed Perkins echoes the views of others: ''If there's a significant advantage -- in fares, schedules or service -- then go ahead.'' But pay for those tickets with a credit card so you'll have a better chance at a refund. He also urges ''frequent fliers with lots of mileage on financially shaky carriers to use it up as fast as they can.''

How safe are airports now? Security is still tight, though the Federal Aviation Administration has been evaluating whether or not to maintain the highest level of security measures, Level IV, now that the gulf war is over. On March 29, curbside check-in for domestic flights -- banned since January -- was reinstated, but luggage searches remain frequent. Parking lots adjacent to terminals were reopened on the same day. But only ticketed passengers are allowed in the gate area and better-trained security guards are scrutinizing tickets.

A sampling of airline tips: -- United. If you're thinking of London, United's service is expected to be special because of its new routes to Heathrow Airport. This month, United is offering double mileage to frequent fliers -- you could wind up with a free domestic ticket. -- TWA. Until July 31, buy any of the 92 Frommer Travel Guides (Prentice-Hall, $7.95 to $18.95), send in the receipt and you'll get a free companion certificate good through July 31, 1992 on a TWA ticket to any destination (except Cairo, Tel Aviv or Las Vegas). There's a $2.50 processing charge and some restrictions on days you can travel. ^ -- Northwest. By earning just 20,000 miles in Northwest's frequent-flier program, you'll get a free U.S. trip. -- Midwest Express. Prices here are comparable to other 21-day advance- purchase fares, but you'll find wider seating and better food in coach than that on many other airlines. -- Delta. Anyone age 62 or older may purchase four one-way coupons for a total of $472 that are valid every day to all U.S. destinations. Unlike most airlines, Delta honors senior discount coupons without advance booking.