By Jayson Blair

Sandy and Christopher Carlson made an offer late last year on a $460,000 one-bedroom loft in the East Village before they had even walked in the door. The Carlsons, who lived in Los Angeles, were looking for a pied-a-terre in New York but did not want to cross the continent each time a broker called.

Because waiting is not an option in the Manhattan real estate market, they took a tour of another kind -- on the Internet -- looking at floor plans and photographs sent by e-mail and taking virtual tours on a Web site.

''I had never been inside,'' Mrs. Carlson said in a recent telephone interview from Los Angeles before her move. ''I just couldn't afford to fly back there every time I heard of something that interested me, and I couldn't afford to stop work for three months and just look out there. So, the Internet was perfect.''

More and more, prospective home buyers and renters are window shopping by computer.

This is particularly true in the New York market, where listings disappear so fast that waiting for the Sunday classifieds can be risky. It also permits house-hunters to view a potential home before even contacting a broker.

The changes are being hailed by customers and most real estate brokerages, but have drawn concern from some individual brokers. They fear that the dot-coms will cut into their business or even make them superfluous, in a world where potential clients could use the Web to contact sellers directly, bypassing brokers.

Web real estate shopping has also spawned its own subcultures, from the prospective renters who check The Village Voice online at 12:01 a.m. five nights a week (when the Web site posts its new listings) to those who take virtual tours and look at the floor plans of luxury apartments and buildings on DouglasElliman.com.

Nationwide, there were more than 3 million homes advertised on the Web in April, compared with the more than 2.4 million listed each month in other places, like classified advertisements.

Analysts say that unlike many new Web ventures, which have high startup costs and low revenues, some real estate sites have already found a way to become profitable by taking a percentage of sale commissions.

Most of the New York real estate sites are run by brokerages, but a handful -- like www.mlx.com, which allows anyone, not just brokers, to list properties -- are independent companies that have begun to move into the market. These companies make money by charging anyone who wants to browse their listings. Some others charge small fees, much lower than standard sales commissions, for listing a property.

''A lot of Internet companies have a hard time making money because they are trying to reinvent the wheel,'' said Tan Chan, the chief financial officer of Corcoran.com, the site where the Carlsons recently bought their apartment.

Corcoran.com has spun off from the Corcoran Group, the real estate brokerage, and will soon move into offices in SoHo. The new company plans to make money by allowing affiliate brokerages worldwide to list real estate on its site. Corcoran.com will receive 25 percent of the commission on any sales that come from its leads, said James W. Kim, the chief executive.

Barbara Corcoran, the president of the Corcoran Group and the chairwoman of both companies, began the Web site with plain text listings in 1994, at a time when the information superhighway was much less traveled. But over the next three years, brokers -- some of whom were not even using e-mail -- began getting calls from clients interested in listings they saw on the Web site.

Since then, Ms. Corcoran has added features like floor plans and a database that allows prospective buyers and renters to search for properties with certain amenities, in specific neighborhoods and within their price range. She has also added photographs, e-mail links to brokers and 3-D virtual tours. Corcoran.com, which unveiled its new Web site in April, has in many ways been way ahead of the curve, according to online real estate industry experts.

Last year, the company received 28,879 e-mail requests and sold 225 apartments to clients who came through the Web site. In recent weeks, the Web site has seen up to 7,500 visitors a day. In New York, selling a home on the Internet can cost a company less than $1 in advertising, compared with hundreds of dollars per sale using the classifieds, company officials said.

For now, there is little worry among those working in newspaper advertising that sales of classifieds will decline because of online real estate sales. The reason is that real estate companies still need to use classifieds, as well as television spots and display advertisements, to draw customers to their Web pages.

But these transformations have already given pause to some brokers who are worried that the online companies are cutting into their commissions.

Information that brokers once provided -- Is this a good neighborhood? Is this a realistic price for a two-bedroom in this area? How do I finance a mortgage on this apartment? -- is increasingly available on Web sites.

Rolf T. Wigand, director of the Center for Digital Commerce at Syracuse University, said brokers ''are trying to find their new role in this process'' because customers can ''partially bypass'' them.

Robert G. Eychner, founder of Eychner Associates, a downtown real estate brokerage, said: ''Everyone has to be on the Internet one way or the other. But there is no replacing the human aspect of having a broker, especially in today's heated market. A computer can't tell you that this is a brand new listing and that it is going to last 20 minutes.''

Mr. Eychner, whose company has been selling in New York since 1982, said part of his job description is being a therapist. ''Buying residential real estate, people really need to talk it through and they need to have someone holding their hand, an adviser who has been through the process,'' Mr. Eychner added. ''There is no computer that is going to help you with a co-op board.''

Mr. Eychner has encouraged his brokers to set up Web pages at the company's site, www.eychner.com, but sees them more limitedly as tools to attract people, particularly international clients.

And Benita Cohen, an independent real estate broker in Gramercy Park for more than 20 years, said the Internet has disadvantages for clients and brokers. Buyers, she said, will often see things on the Internet that are not realistic for them -- and that brokers would not have typically shown them -- and time is often wasted on the properties.

In addition, Ms. Cohen said the Internet would never be an effective tool for the most high-end customers. ''There are properties that never make it out on the Internet, that brokers only hear about over lunch, especially in an insanely competitive market like this,'' she said. ''There is stuff that walks off the table before you could turn on your computer.''

Ms. Corcoran hopes brokers will be willing to give up some of their commissions if Web sites bring additional clients. She also says the Web, by educating buyers about what is available, can cut down on the amount of time the agents have to spend with clients.

Mr. Wigand, the professor and expert on New York's online real estate community, said that because of the exposure the Internet offers brokers on the Web ''sell more and quicker.''

While Corcoran.com has been a leader among New York real estate companies, almost every major brokerage in the city has a Web site with listings, floor plans and other similar features.

One benefit the Web sites offer is speed. And the Carlsons, who are builders, took advantage of it.

Mrs. Carlson flew to New York to look for an apartment last fall after her broker found a one-bedroom loft apartment in TriBeCa. Mrs. Carlson visited the apartment and took pictures for her husband. She returned home and made an offer, but was beaten out by a higher bid.

Mrs. Carlson decided she was not going to let that happen again, and began checking New York real estate Web sites. In early December, she clicked onto Corcoran.com and found another apartment she liked. She called her broker, and asked him to visit the apartment -- at Avenue A and Houston Street -- and take digital pictures that could be sent by e-mail.

The next day, after speaking with her husband, Mrs. Carlson made an offer and it was accepted. ''Normally, I would never consider buying a place without seeing it,'' Mrs. Carlson explained. ''But it is really helpful in the New York market.''

The Carlsons have moved into the apartment, and say that the virtual visit lived up to the real thing.