DEAR BOB: In September, we sold our home for about $144,500. We had to pay off the first mortgage and got about $47,000 cash, which we stashed in the bank. Now we have found a home that we offered to buy for $165,000. The real estate agent took us to see a mortgage lender who will lend us up to 90 percent of the purchase price, or she can arrange a mortgage that is one-fourth of a percentage point cheaper if we take an 80 percent loan. Which loan would you take? Also, if we don't reinvest our full $47,000, will we be in trouble with the IRS on our tax deferral? -- Jon B.

DEAR JON: Most home buyers are better off making a minimum down payment and obtaining the maximum mortgage available. I realize conservatives will argue making a big down payment will minimize the monthly mortgage payment, but in my opinion the slight payment saving is outweighed by (1) conserving cash for emergencies and other investments as well as (2) maximizing leverage profits per dollar invested.

To illustrate, let's compare buying that $165,000 house with $16,500 down payment and a $148,500 mortgage versus a $33,000 down payment and a $132,000 mortgage. At 10 percent fixed interest, the monthly payment on a $148,500 mortgage for 30 years is $1,303.19 versus a payment of $1,158.39 for the $132,000 loan. If you can afford the $144.80 monthly payment difference, and if you take the $148,500 mortgage, then you will have $16,500 extra to spend as you please.

There is no need to reinvest the entire $47,000 from your home sale. All that matters for your IRC 1034 home sale profit tax deferral is that you buy a replacement principal residence costing at least as much as your old home's $144,500 sale price within two years before or after the sale. The amount of cash reinvested is irrelevant. Consult your tax adviser for full details.

DEAR BOB: As a real estate salesman for 14 years, I especially enjoyed the recent letter from the reader whose realty agent cut the sales commission to make the sale possible. Knowing the stupidity and reluctance of my fellow salespeople to cut commissions to make a sale, I loved your reply about submitting the information to the Guiness Book of Records, which has no record of a real estate agent cutting his or her commission. If I might get serious, I would like to point out the right and wrong ways to cut sales commissions. I often make deals with home sellers. If I sell the home myself without another agent's participation, then my commission is 5 percent, but if another agent produces the buyer then my fee is 6 percent. This is fair to the seller and gives me a strong incentive to get the house sold. What do you think about this commission system? -- Rege C.

DEAR REGE: I like it. Too often, real estate agents feel the customary 6 or 7 percent real estate commission is sacred. If the agent has to split the commission with another agent, I agree cutting the commission can be costly. But where the agent doesn't have to share the fee with another agent, a 4 or 5 percent sale commission is plenty in most situations.

DEAR BOB: We live in one apartment of a three-apartment building. As I am well over 55, can I use my once-per-lifetime $125,000 home sale tax exemption or does that just apply to single-family houses? -- Robert N.

DEAR ROBERT: You can use your $125,000 "over 55 rule" tax break on the sales price of your personal residence apartment. However, it does not apply to the profit on the sale of the rental apartments.

To illustrate, suppose your building sells for $500,000, you paid $100,000 for it, and have a $400,000 profit. If the value of each apartment is equal, that means the profit on your principal residence apartment is $133,333.33. Using the $125,000 profit exemption, you will owe tax on only $8,333.33 on your apartment. However, the remaining $266,666.67 profit on the rental apartments will be taxable. Consult your tax adviser.

DEAR BOB: We can pay off our $33,000 home mortgage, at 8 1/4 percent, with money we have in savings. I think we should remain liquid, but my husband is anxious to own our home free and clear. He says we can always get a new mortgage if we need money. What do you think? -- Cora H.

DEAR CORA: Congratulations on seeing the disadvantages of rushing to pay off that beautiful mortgage.

The big drawback of owning a home free and clear is that if you need to borrow on the equity, you may not be able to qualify for a mortgage. This column has contained many sad letters from homeowners who either can't get a loan or who can borrow only at exorbitant rates and terms.

Please, please, please don't pay off your bargain-rate home loan early. Keep your $33,000 in liquid savings even if it earns less than the 8.25 percent interest you pay on the mortgage. You'll sleep much better knowing you have $33,000 in cash readily available.

DEAR BOB: I recently received a $22,000 sales bonus. My wife and I have decided to use it as a down payment on a home. We have been shopping for a home and a mortgage. The problem is that my income as a self-employed independent contractor computer salesman fluctuates wildly from year to year. We have excellent credit, about $14,000 savings, and my earnings will be about $66,000 in 1987. What would be the best way to go about buying a home and getting a mortgage? -- Rick H.

DEAR RICK: Although it's always a good time to buy real estate, you will be getting 1988 off to a great start by acquiring your own home.

However, salespeople and self-employed people often have difficulty obtaining home mortgages because of the uncertainty of their income. But mortgage companies are very eager now to make home loans, so today is an especially good time to buy a home. I've never seen lenders so anxious to make residential loans.

The Boy Scout slogan "Be Prepared" also should be the home mortgage borrower's motto. Have copies of your last two years' income tax returns ready to prove your income. If your 1987 income is substantially larger than 1986, you might want to wait to apply for a home loan until you file your 1987 tax returns. Another secret is to apply with a "portfolio lender" rather than a mortgage lender, who only sells to secondary mortgage buyers such as Freddie Mac or Fannie Mae. Portfolio lenders can be much more flexible than those who sell most of their mortgages in the secondary market.

January is an especially good time to buy a home because in most parts of the United States, the weather isn't good, buyers are still in winter hibernation and sellers are anxious to make a deal. Mortgage lenders are very hungry, too, because the market is slow at this time of year. Shop carefully for both the right home and the best loan. Talk to at least a dozen lenders, starting with the savings and loan or bank where you have your savings account.

DEAR BOB: You told me a few months ago at a real estate investor's convention to buy single-family houses for investment. But I am having trouble finding these properties at decent prices. How can I find a list of the bargain properties like the ones you often buy? -- Ryan H.

DEAR RYAN: Finding bargain properties takes work and persistence. Serious real estate investors ask everyone they meet if they know of any bargains for sale. I often have months when I can't find any good buys. Then several become available at the same time.

Talk to real estate agents, read the newspaper real estate classified ads every day (especially on weekdays when the anxious sellers advertise), and subscribe to local legal newspapers, which list foreclosure default properties. The situation is different in each town, so you need to inquire as to the best source of these bargain properties.

To illustrate, my banker told me recently about a customer who bought an apartment building worth $1 million at a sheriff's sale for less than $700,000. While bargains like this don't become available every day, persistent searching for them can be very profitable.

DEAR BOB: In October, we bought a condominium town house. As you often suggest, we carefully checked the sound-proofing and found no problem. The grounds are well-maintained and the residents we talked to seemed very happy. But on Nov. 1, we received a notice of a $2,000 special assessment to pay for maintenance costs, such as roof repairs, painting and drainage. The residents knew about this proposed fee last August, but neither the seller nor the real estate agent, who lives in the complex, told us about it. Do we have any legal recourse? -- Genny H.

DEAR GENNY: Shame on you for not investigating the financial status of the condo owner's association. But numerous court decisions require real estate sellers and their agents to tell prospective buyers of all material defects affecting a property. A proposed special condominium assessment falls within this disclosure rule.

However, if you sue the seller and realty agent for damages because of failure to disclose the $2,000 special assessment, your legal fees can easily exceed the amount of your damages. Consult a real estate attorney, but don't get your hopes too high.

DEAR BOB: My husband and I are debating whether to remodel our home or buy a larger house. We like our neighborhood and the kids are doing well in excellent schools. But we need to add an extra bedroom and remodel the kitchen. The cost will be about $20,000. Is this a better investment than buying a new house in an unknown neighborhood? -- Karla C.

DEAR KARLA: Why upset the apple cart? If you like your home and neighborhood, it's usually easier and cheaper to remodel your home than to buy a new one. However, don't over-improve. Be sure the cost of the work you plan will add at least $1 of value for each $1 spent.

DEAR BOB: My wife and I want to buy a home. A few weeks ago we saw a house we both liked and we agreed to make a bid. But the obnoxious real estate agent insisted we make a $5,000 good faith deposit with our offer. As we were offering $92,500, I thought $1,000 would be more reasonable. The result was we didn't make the offer. Is it customary to require such a large deposit? -- Ernie N.

DEAR ERNIE: You raise a very touchy subject. Legally, no earnest money deposit is required because a binding contract can be formed if the buyer and seller sign the sales contract. However, most sellers will not accept a purchase offer bid without a reasonable good faith deposit.

Most real estate agents will tell you the larger the buyer's deposit the better the chances the seller will accept the offer. Put yourself in the seller's shoes. If you received an offer bid with just a $1,000 good faith deposit, you wouldn't be convinced of the buyer's sincerity. But if the offer contained a $5,000 deposit, which the buyer could lose if the sale isn't completed, you would feel more confident the sale will close.

Experienced real estate agents strongly encourage buyers to make as large a deposit as possible. However, in my opinion, that agent should have backed down, taken the $1,000 deposit and let the seller decide if it was acceptable. When a seller is highly motivated, the deposit size doesn't matter. I recall, for example, buying a $100,000 investment property with just a $100 good faith deposit. As a seller, I would never accept such a low deposit, but who knows what motivated the seller to accept my offer?

In the future, make whatever deposit you wish with a home purchase offer. However, don't forget that a large deposit can often entice a reluctant seller to accept an otherwise undesirable offer.

DEAR BOB: I have noted several recent questions in your column involving Starker delayed tax-deferred exchanges. The readers were complaining about not being able to find CPAs and attorneys familiar with this type of investment property exchange. As I live in a very small town, I had the same problem until I phoned the Board of Realtors in a nearby city. They offered me names of about six agents who handle exchanges and they also referred me to several real estate attorneys and CPAs who know how to do Starker exchanges. As a result, I have no trouble trading my income properties in delayed exchanges. -- Kathryn C.

DEAR KATHRYN: Thank you for sharing this excellent source of information. My experience has been that some Boards of Realtors are very helpful to public inquiries. But too many Boards of Realtors have clerks who are not very helpful, probably feeling they are to serve only their Realtor members.

For example, most Boards of Realtors will not give out names of members who specialize in particular types of sales, such as lots, farm land, recreational property and commercial property. Nor will most Boards of Realtors give the names of their top sales volume members. In my opinion, this is a disservice to members as well as the general public requesting this information.

DEAR BOB: We are trying to buy a home in a very small neighborhood where homes rarely come up for sale. Our real estate agent told us about a house that the owner wants to lease for two years, but she will give us an option to buy at the end of two years. She is offering a 50 percent rent credit toward the option price. We like the house very much but are turned off by these unusual terms. Do you think we should go along? -- Joseph L.

DEAR JOSEPH: That sounds like a good deal. I can't advise on the desirability of a specific purchase, but if you like the house, grab it before a bargain hunter does.

Although you won't get any tax deductions for mortgage interest and property taxes, that 50 percent rent credit toward the down payment sounds even better.

I'm guessing, but perhaps the seller wants to delay the sale until she becomes 55 and is eligible for the $125,000 "over 55 rule" home sale tax exemption. A lease-option is a great way to accomplish this.

DEAR BOB: I want to buy a small house for myself and my 4-year-old son. As I don't have much cash for a down payment, I can't be too fussy. My father found a nice home in the best school district. However, the floor plan is bad because the bathroom is located off the kitchen. But there are two bedrooms, so I could have one and my son the other. The price is not a bargain, because of the top location. Do you think I should buy despite the bad floor plan? -- Charlotte C.

DEAR CHARLOTTE: I have purchased many houses with bad floor plans but with other redeeming qualities, such as good location, which outweighed the drawbacks. However, some mortgage lenders will not make loans on houses with incurable defects so, if you decide to buy, be sure your purchase offer contains a mortgage contingency clause.

I owned a house where the residents had to walk through the kitchen and the back porch to reach the bathroom. Surprisingly, no tenant ever remarked to me about the floor plan. Nor did the lender. People will put up with functional obsolescence if the home has other benefits, such as a top quality school district.

DEAR BOB: We made an offer to buy a home. After reading your columns, I knew our offer should contain a mortgage finance contingency clause. But the real estate agent was very indignant when I insisted on specifying the exact terms we wanted in our mortgage. Since the agent was so negative, I also insisted on putting in the offer, as you have suggested, "This offer to be presented to seller only in the buyer's presence." I'm glad I put that clause in the bid, because the listing agent was very hostile. But the seller accepted our offer anyway. Then we changed our minds and now want an adjustable-rate mortgage rather than the fixed rate specified in our contingency clause. Now the seller is trying to get out of the sale by saying since we didn't even apply for the loan we specified, the sale is off. Do you agree? -- Myla R.

DEAR MYLA: No. The mortgage finance contingency clause is for the buyer's protection. It is not for the seller's benefit. By accepting an adjustable-rate mortgage instead of the fixed-rate loan you specified in the mortgage finance contingency clause, you waived your protection under the finance contingency clause. I see no way the seller can use that clause to get out of making the sale to you.

Your letter emphasizes an important clause all home buyers should put in their home purchase offers. The finance contingency clause should specify exactly the mortgage the buyer needs to make the purchase. For example, such a contingency might say: "This purchase offer contingent upon buyer and property qualifying for a new first mortgage of at least $100,000 with a fixed interest rate not exceeding 10 1/2 percent for at least 30 years with a loan fee not more than 2 points and a monthly payment not exceeding $914.73."

However, since the finance contingency clause protects the buyer, not the seller, the buyer is free to obtain another satisfactory loan and waive the clause's protection. Consult a real estate attorney.

DEAR BOB: My brother and his wife signed a contract to buy a new home. But a few weeks before the closing, he got a job promotion out of town. So I told him my husband and I would buy the house because as we had seen it and like it very much. The mortgage company approved our substitution as borrowers. However, the builder says we cannot take over the purchase contract because his prices have increased by $5,000 since my brother and his wife signed their purchase contract. I think this is a rip-off because the builder knows we really want that house. How can we take over my brother's purchase contract at the lower price? -- Kathy L.

DEAR KATHY: Your question involves basic contract law. The general rule is that all contracts are assignable unless (1) prohibited by the terms or (2) it is a personal service contract.

Presuming your brother's purchase contract did not prohibit assignment, the issue then is whether or not the builder accepted the original buyers because of their personal qualifications such as income and credit history. If the builder checks all prospective home buyers for their income and credit background, or if he was helping finance the sale such as by carrying back a second mortgage, then it is arguable this is a nonassignable personal service contract.

One way to solve the problem is for your brother and his wife to buy the house and then immediately sell it to you for the same price. However, be sure the lender will let you assume the mortgage. Consult your attorney for full details.

Readers with questions should write Bruss directly at P.O. Box 6710, San Francisco, Calif. 94101.