Question: What do you think of the six-month "T-Plus" certificates now being offered by local savings institutions? It looks to me like a great opportunity for a high return with complete safety.

Answer: As you say, these new money market certificates are safe and offer a high return. But it isn't necessarily a great opportunity; as with every other type of investment, it depends on your particular circumstances.

There are some minor drawbacks with these special six-month certificates. The interest is "addon," while the return on the Treasury bills on which they are based is a "discounted" rate. And the income from the Treasury bills is exempt from state and local income tax, while the certificates are not. (Both are subject to federal income tax.)

Another drawback is the fact that the minimum purchase is $10,000, which puts these certificates out of reach for a good many people. (A few brokerage houses are now offering a unit investment trust which pays a little more than these certificates and which is available in $1,000 units.)

But these are not really major disadvantages. In terms of investment strategy, the significant problem is the six-month term. What are you going to do with the money when you get it back six months from now?

If interest rates then are as high as or higher than they are now, purchase of a certificate now turns out to be a pretty good move. But if rates are lower, then you missed a chance to lock up for the long term a historically high rate of interest, available now with high-quality bonds or bond trusts.

In spite of the many statements by experts in monetary matters, no one can predict with any certainty where interest rates are going to be in six months. For what it's worth, my guess is that longterm rates are going to be down from one to one-and-a-half points by spring.

That uncertainty is precisely the point. These certificates are ideal as a parking place for funds you expect to need in a relatively short time-as a down payment on a new house nex spring, for instance.

But if you're looking for income for the long haul, then pruchase of a six-month money market certificate becomes a speculative investment. In effect, you're gambling on the movement of interest rates betwen now and next June.

This has got to conflict with your basic investment philosophy. Buyers of CDs and other high-quality fixed-income investments are, almost by definition, conservative and oriented primarily to safety of principal.

If i'm right about the movement of interest rates then you will have traded an extra point or so in interest over a six-month period for the loss of a point or so over the nex 10 to 20 years-not a very good trade. More important: You'll have to "sweat out" interest movements for the nex six months-exactly the kind of thing a conservative investor treis to avoid.

Q: In a recent article you said that if bonds are not redeemed when dur, then you have a capital loss. Is this short-term or long-term? Since a bond is really equivalent to a loan, it seems to me that failure to redeem would make it a bad debt, which is always treated as a shor-term loss.

A: True-a bond is equivalent to a loan to the issuing corporation. Also true-a defaulted non-business loan creates a short-term capital loss.

But to most people-and, more important, to the IRS-a bond is a form of investment, and follow the rules for investment property rather than for personal loans.

That is, the determination of short-term versus long-term derives from the holding period. If you owned the bond for 12 months or less, it's a short-term loss; more than 12 months, you have a long-term loss.

And you use Dec. 31 of the year of default as the date of the loss-not the actual date the bond was due for redemption.

Q: I understand that the new tax law authorizes a larger exclusion on capital gains than in the past. I have a second trust on property I sold a few years ago. Do I still have to report 50 percent of the capital gains portion of each payment?

A: No. If you sold an asset on the "installment plan," payments received after Oct. 31, 1978 qualify for the new 60 percent exclusion (on the capital gains element only, of course) even though the sale itself took place before Nov. 1.