A tight supply of houses for sale, along with rising prices and worries about higher mortgage rates, is making buying a home a challenge in some areas this season.

Because of a lack of inventory of homes in some markets, there is often a rush of offers when properties do become available, said Javier Vivas, manager of economic research at Realtor.com, a listing website. "Buyers," he said, "should expect heavy competition."

The median sale price for previously owned homes in April nationally, according to the National Association of Realtors, was $244,800, up 6 percent from a year earlier.

"Demand is easily outstripping supply in most of the country, and it's stymieing many prospective buyers from finding a home to purchase," Lawrence Yun, an economist for the Realtors association, said in a statement about the housing market.

An improved economy has stimulated demand for housing, but the supply of homes for sale has lagged, making it harder for shoppers to find affordable properties, said Daren Blomquist, a senior vice president with Attom Data Solutions, which tracks property trends.

One factor in the tight supply, Blomquist said, is that people are holding onto their homes longer than they once did. Investors who bought homes during the recession are earning rental income and are not in a rush to sell, while some owners still cannot sell because they remain underwater on their mortgages — meaning they owe more than the homes are worth. The average home seller these days has owned the house for about eight years, he said, compared with about four years before the recession.

Another factor, according to Attom's data: fewer foreclosures. Nearly 10 years after the financial crisis, foreclosures are at prerecession levels in many areas, reducing another source of homes for sale.

All that means that competition is fierce in some markets, especially for lower- and midpriced homes, and home shoppers must be nimble. Lynn Johnson, a broker with Bamboo Realty in bustling Raleigh, N.C., said buyers must understand that they do not have days to mull an offer. "They have to be ready to pull the trigger if they find the right house," she said.

Buyers must also be prepared to put more cash down when they place a property under contract, she said. In the past, Johnson said, shoppers could expect to put down $500 as a "due diligence" deposit to the seller, which they would expect to lose if they found a house they liked better and walked away from a purchase contract. But now, sellers may demand deposits of $1,000, and sometimes as much as $2,500.

In Denver, where the inventory of homes has been low for the past couple of years, "There is no such thing as lowballing," said Stacie Staub, founder of West and Main Homes in Lakewood, Colo., near Denver. Often, she said, homes go on the market on a Friday and are under contract by Sunday.

The market is so tight that Staub often recommends that people looking to trade up to a new home should first sell their own house, and then go shopping with cash. Sellers generally frown on "contingency" offers, which are subject to the sale of an existing home. When sellers are receiving multiple offers, they will choose all-cash bids over contingency offers, she said: "If you can't pay cash, it's harder to get your offer accepted."

Buyers are often so eager that sellers can negotiate a two-month "rent back," she said, so they can live in their home — often rent-free — while shopping for a new one, Staub said.

Even markets that had not been so cutthroat are starting to shift. The area in and around Fayetteville, N.C., had been "medium warm" earlier in the spring, but activity has heated up. A lack of new construction has helped to tighten inventories.

Here are some questions and answers about the current homebuying market:

Q: How should I approach house shopping in a tight market?

A: Johnson advises clients to write out a list of "needs," or must-haves, and wants, to streamline their house-hunting efforts. "You cannot waste time," she said.

Brokers say shoppers should expect that sellers will receive multiple offers. This means that if you find a house you like, you should make your best offer right away. Many shoppers want to offer the list price or below, but in a seller's market, homes often sell for more than the list price.

Q: What should I expect will come with the house?

A: In calmer markets, buyers typically expected to get major appliances like refrigerators, washers and dryers — perhaps even that riding lawn mower sitting in the garage — with the purchase of the home. Not so in a seller's market, Johnson warned. "You are getting the house," she said. Appliances, and usually closing costs, are most likely on you, she said.

Q: What are mortgage rates doing?

A: Rates are still low by historical standards, tough up a tad from a year ago, reducing some of the pressure from rising home prices.

Ann Carrns writes for the New York Times.