TTax time is just around the corner, with 26 days left before federal income tax returns must be in the mail. If you want help figuring your taxes, the Internal Revenue Service will assist you. IRS employes will answer questions by telephone, provide tax publications or advise you in person at the agency's offices in Wheaton or Suitland.

If you cannot fill out your return, the IRS will do it for you. Forms are available in Spanish, Chinese and Vietnamese. In addition, the IRS has new "problem resolution representatives" who will untangle red tape and help if someone else falls down on the job.

All of the IRS services are free.

There's more good news. The filing deadline has been extended this year from April 15 to midnight of April 17, because the 15th falls on a Saturday.

The toll-free number for tax help is 488-3100. Deaf persons with access to a TV phone/teletypewriter (TTY) have a special number: 1 - 800-428-4732.

Although the IRS has simplified this year's form, the agency still expects crowded offices and clogged telephone lines during the final days before the filing deadline. You are more likely to get prompt service by telephoning on a Wednesday, Thursday or Friday before 9:30 a.m. or after 3:30 p.m. If you make a personal visit, go toward the end of the week, the agency advises.

IRS tax advisers sometimes make mistakes. The agency is not responsible for the accuracy of your return, however, even if an IRS employe prepares it for you. That means you may have to pay more, if you are audited later, but you will not have to pay interest on the additional tax if the IRS preparer makes a mathematical error on your return.

Here are IRS recommendations on where to go for help, how to prepare for an IRS interview, records to keep, free tax publications, where to complain about refund problems and how to handle an audit. Where To Go For Help

The taxpayer service office in Wheaton is located in Plaza South, Wheaton Plaza Shopping Center. Parking is free and handy, right outside the ground floor entrance. If you simply want tax forms, turn left as you enter the building. You may pick them from a rack or ask the attendant for help. The receptionist is located at a desk straight ahead, as you enter. She will give you a card that indicates the type of service you require: yellow for questions only, pink for help with the short 1040 A form, and blue for the long 1040 form. Be sure your card corresponds to the kind of service you seek.

Advisers answer questions at a counter with dividers which provide some privacy. If you want help on the long 1040 form, you will be taken to a table away from the crowd. Count on spending an hour, in addition to waiting time, to have your long 1040 form prepared.

The Suitland office is located in room 204, Penn Silver Building, on Silver Hill Road. Parking in the back of the building is free. The office has a public telephone line linked directly to the main taxpayer service answering system in Baltimore. You may use this telephone instead of waiting to talk to an employe in the Suitland office, if you are in a hurry. Otherwise, the routine followed is the same as in the Wheaton office. However, there is no special counter for questions. Preparing For Your Interview

Help on the long form will require some homework in advance. First, study the form you wish to use and make a list of all the information required. This will include your social security number, number of dependents, types and amounts of income and expense incurred during the the year. If you plan to itemize deductions, write down the amounts of the deductions and reasons for them.

Take the list and your W2 form (the wage and tax statement provided by your employer) to the IRS office. Your helper will explain each line of the return and complete it for you if you cannot do so yourself. Do not take a bundle of cancelled checks or receipts with you. Your helper cannot go through them for you.

When the form is filled out, the employe will have it verified by someone else, sign it as the preparer, have you sign it and then give you a copy for your files. The IRS will retain the original of your return.

Since the law is complex, and mistakes are easy to make, you should be on guard against incorrect IRS advice. If you believe the employe is wrong, speak up. Ask to see the law that affects your case. Record Keeping

After your return is prepared, keep a copy for your files. In addition, keep all documents that substantiate the claims you made on the return. These include sales slips, invoices, receipts, cancelled checks and other financial papers. To be convincing, the documents must clearly establish reasons for the deductions and credits shown on your return. Also, make a note for your file describing exactly how you or your IRS helper solved any special problems (such as the sale of your house). If your are audited you may have to reconstruct the way you figured your taxes long after you have forgotten how you did it.

Because the IRS can audit your return any time within three years after it is due or filed, whichever is later, you should keep most records at least that long. You may have to retain other documents indefinitely. For example, you will need files relating to the purchase of a house, and receipts for any improvements made to it, in order to calculate taxes if you sell it later. Free Tax Publications

If you want to prepare your return yourself, but have some special tax problems, you might consult one of the 84 free booklets put out by the IRS. They cover a broad range of topics and explain tax problems in detail.

For example, Publication 523, "Tax Information on Selling or Purchasing Your Home" (16 pages), contains a comprehensive example of a home purchase and sale, special rules for persons over 65 and a sample filled-in Form 2119 "Sale or Exchange of Personal Residence." Publication 553 (12 pages) has up-to-date information on 1977 changes in the tax law. Publication 526 (eight pages) gives rules for income tax deductions for contributions.

The entire list of booklets appears on the last page of "Your Federal Income Tax," (Publication 17, 192 pages). This is the agency's popular and comprehensive tax guide. It compares favorably with commercial newsstand guides that sell for $3 or $4, and it is free.

One note of caution: IRS publications explain only the official government interpretation of the tax law and not the more liberal views that courts have taken on specific cases. Also, you may not rely on any IRS publication as your authority in tax matters. Even if you follow the official guide, the IRS can challenge you, take you to court and win. The same is true of commercial guides. Trouble With Your Refund

Your refund should arrive four to six weeks after you mail your return. If the IRS does not send your refund within 45 days after your return was due or filed (whichever is later), it must pay you 6 percent interest on the total amount it owes you. This year, interest will begin on June 2 if you file on April 17.

The IRS gets more complaints about refunds than anything else, the agency reports. Your check may be delayed, missing or stolen. It may be larger or smaller than you expected, or it may, not arrive at all. If the check does arrive, but is for the wrong amount, wait for two weeks, the IRS suggests. You should get an explanatory notice within that time. If you do not receive an explanation, or if your refund does not arrive at all, the IRS suggests you take the following steps.

1. Call the toll-free number, 488-3100. Keep a record of the date, time and name of the employe you speak to and copies of any documents you are asked to send to the agency. Explain the problem and tell the employe your home, address, social security number, telephone number and the date you mailed you return. If the employe does not ask for this information, nothing is likely to be done about your complaint. Find out when the employe intends to return your call or mail necessary forms to you. If you do not receive the expected call, or if the forms do not arrive, take step two.

2. Call the toll-free number and ask for the problem resolution representative. This person's job is to help taxpayers who have tried but failed to get assistance through normal channels. If after five days you have not received a satisfactory response, take step three.

3. Call the toll-free number and ask for the taxpayer service group supervisor. Regina Knight. If you are not satisfied with the response, take step four.

4. Call the toll-free number and ask for the chief of the taxpayer service division. Charles W. Brooks. If your problem is not solved at this level, take step five.

5. Write to the district director, the top IRS official in this area.Explain the problem and each step you took to solve it. Send your letter by registered mail, and request a receipt. Write to: Gerald Portney, IRS District Director, 31 Hopkins Plaza, Baltimore, Md. 21201.