Because of the stock market crash, are you rethinking whether to use a discount broker? Many discounters' customers think they didn't distinguish themselves in the crisis.

Frantic investors jammed the telephone wires of the big national discounters, such as Charles Schwab & Co., and got busy signals. Although thousands of customers got through, thousands more couldn't reach their brokers. As a result, they couldn't sell stocks that were going down or buy stocks that looked to them like bargains.

A certain number of busy signals were inevitable, given a 604 million-share day like Black Monday. But Scott Staps, a spokesman for the North American Securities Administrators Association (NASAA), said: "We've heard of extreme cases where people couldn't get through {to their brokers} for five to seven days."

The NASAA has set up a toll-free telephone number to receive post-crash complaints about brokers, both discounters and full-service firms. By Friday, Dec. 4, it had received about 6,200 calls. (Dial 800-942-9022, and keep on trying if it's busy!)

Errors and late trades occurred at all kinds of firms, and couldn't be helped because of the crush.

Some smaller full-service firms have been accused of deliberately not answering their phones, to avoid taking sell orders in the stocks of risky companies they had brought public.

The telephone problem may have been greater for discounters because they run a tighter ship than the full-service brokerage houses, according to Mark Coler, co-author of "70 Percent OFF! The Investors' Guide to Discount Brokerage."

Discounters -- who chiefly take orders for trades you've already decided on -- are wired for short telephone calls. Full-service firms, by contrast, expect their brokers to spend time with customers on the telephone -- giving advice, signing up new clients and selling products. So their telephone backup is deeper.

But one or two day's problems with busy signals shouldn't be enough to send you to a full-service broker, who will charge much higher commissions on trades. Try the following strategies first:

Get an automatic redialer for your telephone, one that will keep on trying a busy number. The more often you dial, the better your chance of slipping through.

If the firm has a 24-hour phone number, call it at the crack of dawn. Your order won't be executed until the market opens, but at least you'll get it in.

Sign up with a small local discounter (if there is one in your community) rather than one of the national firms. A small firm is less likely to be overwhelmed by calls.

Show up in person. The wait usually isn't long.

Know your broker's rules. In a volatile market, the broker might insist on having the stock certificate in his hand (or sufficient equity in your account) before he sells. In addition, you might have to write a check in person (or have the money in your account) before the broker will execute a buy order.

Keep an account with more than one discounter -- maybe a big one and a small one -- to give yourself a choice.

Using two firms makes sense even in good times, because of the different ways brokers charge for their services.

One discounter may be the lowest cost if you're selling high-price stocks, while another does better on low-priced stocks. They charge different minimums for small orders (ranging from around $23 to $50). Some charge by the share (a "sharebroker"), while others charge by the dollar value of the purchase (a "valuebroker"). Doing business with two firms gives you a better chance at paying rock-bottom commissions.

Pacific Brokerage Services of Los Angeles is a good example of a low-cost, no-frills company. Charles Schwab offers many more services, but charges some of the higher prices in the discount world. Bank-connected discounters, such as Security Pacific Brokers, are also likely to charge on the high side.

Coler is updating the list of discounters that first appeared in his 1983 book. For a copy, send $12 to Mercer Financial Services, Suite 800, 80 Fifth Ave., New York, N.Y. 10011.